If bicyclists actually did yield to pedestrians, as the law requires, it wouldn't be a problem. And by yield I mean fucking yield. I think in the minds of bicyclists with a rough notion of what the rules are, if you didn't actually send the pedestrian sprawling, that's yielding.

And then there are the significant number of bicyclists who clearly believe that when they yell, or ding a bell, the pedestrians ahead are required to get the hell out of the way.

In other words, for all the shit that bicyclists say they get from cars, they give the exact same shit two times over to pedestrians.

So fuck bicyclists. Let them figure out a way to clean their own house and enforce some kind of civil behavior on themselves. Bicycling licenses or public beatings or some damn thing. Let them work it out. Until they do that, fuck them all.

I know you're in Omaha, but it's legally fine in Seattle if you're biking on the sidewalk, as long as you are yielding right-of-way to pedestrians.

Specifically, Seattle Municipal Code states:

Section 11.44.120 RIDING ON A SIDEWALK OR PUBLIC PATH. Every person operating a bicycle upon any sidewalk or public path shall operate the same in a careful and prudent manner and a rate of speed no greater than is reasonable and proper under the conditions existing at the point of operation, taking into account the amount and character of pedestrian traffic, grade and width of sidewalk or public path, and condition of surface, and shall obey all traffic control devices. Every person operating a bicycle upon a sidewalk or public path shall yield the right-of-way to any pedestrian thereon, and shall give an audible signal before overtaking and passing any pedestrian.

above from http://www.seattle.gov/transportation/bikecode.htm

Additionally, Revised Code of Washington indicates:

RCW 46.61.261 - Sidewalks, crosswalks -- Pedestrians, bicycles.

The driver of a vehicle shall yield the right of way to any pedestrian or bicycle on a sidewalk. The rider of a bicycle shall yield the right of way to a pedestrian on a sidewalk or crosswalk.

above from http://www.seattle.gov/transportation/pedrcw.htm

But as the others have stated here, it really depends on the sidewalk. Some sidewalks are typically heavily used by bikes, some aren't. If there are a lot of people around then don't ride too fast and/or be a jerk.

There are many times though in which I wish a bicyclist were on the road instead of the sidewalk. One reason biking in the road can be dangerous is because car drivers don't want to or don't know they need to share the road. If there were more bikes in the road then maybe they'd get the hint that they need to share. Instead, the bicyclists stick to the sidewalk and drivers think that's where bikes belong. And then pedestrians get annoyed with the bicyclists. Ideally, the bicyclists could safety ride in the road.

First of all, you have a RIGHT to the road. Use it!

Almost everyone else has addressed the problems that cyclists on the sidewalk cause for pedestrians, but if you look at it from a completely selfish perspective, it's a poor idea to ride a bike on the sidewalk because it is the LEAST safe place to be, according to studies (http://bicycleuniverse.info/transpo/almanac-safety.html):

"Riding on the sidewalk is several more times more dangerous than riding in the street. (William Moritz, 1998) Another study says it's twice as dangerous. (Bicycling Life, 1985-89)"

Cycling on the sidewalk creates the illusion of safety. Since people THINK they're safer on the sidewalk, they tend to drop their guard for potential hazards. Also, drivers aren't expecting you to ride your bike on the sidewalk, so they'll pull quickly into and out of driveways. They'll look for pedestrians (sometimes), but mostly drivers are looking for other traffic without checking the sidewalk.

Most cycling accidents occur at driveways and intersections. So if you MUST ride your bike on the sidewalk, you should also know that you're putting yourself at more risk being there than on the street.

I have to say, as a motorcyclist who has nearly laid my bike down several times from bikers going from street to sidewalk to street again, right in front of me, I would like it if bikes would stay to one or the other. I don't really care which one.

If you want to be on the road, follow the rules of the road. If you're traveling along at break-neck speeds, and then immediately become a pedestrian, so that you can cross a street in the cross-walk, and then soon after that, cross the street again, this time between intersections, only to get back in the car lane, and zoom on to the next intersection, for the sole-purpose of getting somewhere faster, and not have to use your breaks, I will always honk my air-horn at you, and try to scare the living crap out of you. I might even swerve to keep you from passing me a third time in the same manner.

I completely understand the thought that everyone is out to get you. Again, I am on a motorcycle, and constantly aware of my intrusion upon people's sensibilities, simply because I drive through their neighborhood. I also understand that if you are a jerk, no matter what you drive, ride, run, cycle or row, you are going to be a jerk there too. And you probably make little jerks along your path through life as well.

Try to realize that, like you, we all have somewhere else we would rather be. But without order, there would be no peace on the road. Follow the rules, and feel free to ride on the sidewalk, or in the bike lane, or in the auto lane, as much as you like. Just do it with some respect for others.

And please, if there is a bike lane, use it. It's there for you, and to keep you and pedestrians safe. I can't speak for every driver out there, but I see you better if you're where I expect you, and I expect you in the bike lane, if there is one.

Be respectful of pedestrians and be aware that there are a lot of blind corners that wouldn't exist if you were in the road (i.e. driveways and hedges, brick buildings, etc.) If you're going around any corner, you should assume another cyclist going your speed is doing the exact same thing - if you're going to fast to stop yourself from hitting your twin, then you're going to fast.

But I understand riding on the sidewalk. I prefer to be in the road, but there are certain stretches of standard arterials here in seattle where drivers treat them like they are freeways. I've also been harassed by enough cars (again on certain stretches) that I just opt for the less-likely-to-get-killed pathway.

For having such a bike friendly mayor and city council, there are a lot of really anti-cyclist drivers.

As somebody who walks to the bus stop every weekday and who tends to deal with uniformed bike commuters (you know, bright yellow jacket and black spandex[?] pants), my first instinct is along the same line as elenchos's.

You can bike on the road and bike lanes are (ostensibly) there for a reason.

I think I get wanting to be safer from drivers though (drivers...bah).

So to answer your question, riding on sidewalks is "so bad" mostly because many bicyclists ride like drivers drive - as though everyone else is just a worthless peon trespassing on their God-given right-of-way.
Don't bike like a dick (i.e. bike responsibly as per stinkbug, e.strange and Little Red Ryan Hood), and you're cool.

Also, you're in Omaha and from what you say it's a non issue.
So there.

On certain streets I ride on the sidewalk and don't see anything wrong with it. Like you, I do this on streets where I feel safer on the sidewalk then I do on the street, but another factor in this is the sidewalks where I ride don't have lots of foot traffic.

Sidewalk riding is so bad if you are bumping into walkers or separating groups. As e.strange said the Seattle bike cops always seem to sidewalk ride and it is extremely annoying because they always seem to assume the right of way. If you're going to ride on the sidewalk be sure to be totally aware of everyone around and don't knock into them, ride slow (a bit faster then a walking speed is okay but don't treat it like a race), and get out of the way for groups.

Also be sure to avoid blind driveways, if you were in the street you'd be easier to see, on the sidewalk it might be too close.

It's perfectly fine to bike on the sidewalk—and legal! Be super respectful of pedestrians and don't react when they yell at you anyway (because they will). I bike on the sidewalk a lot; I think it's a relaxing alternative to higher-speed street cycling. Sometimes you just want to roll along at your own pace and not worry about insane drivers. See you on the sidewalk!

It's legal, and a good idea if you're not a hardcore biker. I meander when I ride, and prefer the sidewalks. People around here drive like maniacs and half the time are too busy texting to watch the road. I'll take my chances with irate pedestrians, thanks... Especially downtown, where my husband and my sister have both been victims of hit-and-run while biking the street.

I do it, too often. We have angle parking on one of the main streets here, and I feel really unsafe riding behind all those parked cars. The MOVING traffic is within inches of me (although everyone is moving pretty slowly), so I go on the sidewalk a lot more than I should. Haven't had any problems, but I would if there were more riders.
In addition, there's a college campus here, and their sidewalks are all wide enough for snowplows and wheelchair vans, so there's never a problem there.

A: if you are 8 years old, it's fine.

A to your 2nd Q:
because ignorant rider/operators too often make the sidewalk unsafe for peds, dogs, kids, etc and that can be illegal in addition to selfish-little-bitch behaviour.

biking on the sidewalk at street speeds can be cited as illegal (reckless driving, for example).
There are specific rules for biking on the sidewalk; namely, yielding to all peds as if you are operating a vehicle (which you are), and audio alerts EVERY time you pass from behind.

Biking on the sidewalk? Fine. Go slow FFS. The sidewalk is not a de facto passing lane to get around danger zones on the street.

Are you kidding???? Well, for one thing, it is dangerous to pedestrians, and that includes children, the elderly, and the pets who are being walked on leashes. Just this morning my dog and I nearly got wiped out by a selfish bike rider, who careened around the corner of my apartment building without bothering to slow down, look ahead, or even CARE about what was around the corner. I am now committed to attempt to change the laws in the city of Seattle. I have lived in New York, Boston, Sydney, Australia, Melbourne, Lousiville and NEVER have I heard of a city that allows this stupid behavior. Well, welcome to the city of Seattle. This is just another entry on my list of why I can't stand it here!