Without getting too "Mr. Pink" here, I think this whole "tipping automatically thing; it's for the birds". That said, I still find myself in the apparently small minority ponying up nearly the full normal amount, for the following reason:
I remember getting really irked one time when I was getting takeout (Cafe Minnies' Tomato Basil soup) and finding that they'd charged me a 15% "takeout fee" - not to cover the cost of the bowls/spoons/etc, but to cover the lost tax revenue for the servers.
I guess the restaurant had been "estimated" by the IRS as having an average of 15% in tips - therefore, for any server's transaction where they DON'T get tipped, they are (potentially) losing money, unless they meticulously document all year (which, I guess it could be expected that Cafe Minnies' servers did not). Not to mention that most waitstaff "tip out" their busboys, cooks, bartenders, etc.
I personally actually hate tipping for all the reasons everyone else does - it's unfair to "fast-food" staff, it obscures the cost of food (the Ticketmaster effect), it introduces the concept of guilt & expectation, cajoling and power-play, into something that normally would feel like a delight.
I hate that if I DON'T order booze immediately (or god forbid, ask about using a discount card), I'm immediately profiled as a "bad tipper" not worthy of good service (even though despite this self-fulfilling prophecy, I pretty much always tip well anyway, if only to counter the stereotype).
My girlfriend was once followed out of Bimbo's and harrassed by an utterly incompetent and inattentive server after leaving *only* a 10% tip. (Believe me, she's not cheap - you'd have to hear the full story to realize how outrageous this was).
Point is, the way I see it is that given the system servers are in (which I wish I could change), I generally tip somewhere in the ballpark of 20% (in cash, whenever I can), UNLESS THEY'VE PROVIDED ME DEMONSTRABLY BAD SERVICE - even if the amount of that service is no more than bagging up some styrofoam or popping open a can of Rainier.