Ben Franklin wrote this Way, too. His autobiography is full of capitalized Nouns.

I agree with Fnarf's Idea about the German Influence. Plus, Typing this Way is kinda fun. Camel-Case-Light, I guess.

I'm not sure why you're knocking Milne: It's not like he was responsible for writing 'CATHY'.

I often use caps on verbs and nouns to pretend as if they are a Very Official Thing. The kinda thing you might throw a trademark onto.
Perhaps I do this because I'm Milne-influenced, or more likely, I'm people-who-like-Milne -influenced. I have no qualms about using my shift key in This New Fashion. I try NOT to use it for things that would otherwise be better served by italics, all-cap or bold.
I especially like to "Random Cap" anything that I think might do double duty someday as a Booktitle, name of a sitcom, or a new one-hit-wonder band.

And indeed, many blog and even Stranger writers throw both caps and Bolds at us randomly, so IMO there's a cultural momentum to it.

Note also: this practice is extrememly common in Ye Olde Time letters of the 1700's and 1800's. Both actual, fictional, (and harlequin romance-al). Napoleanic-era fiction, especially, Loves This Shit

Verily.

elenchos, I do sometimes capitalize phrases mid-sentence for emphasis.

Where did I learn it? Perhaps subconsciously, from phrasing such as 'Trouble with a capital T' or something similar. I cannot tell you for certain where or how I picked up that usage.

I tend to do it to emphasize sarcasm, myself ("Society will crumble if The Gayz can marry."). But there are definitely those who use a very Germanic or archaic-English style of capitalizing most common nouns. It drives me berserk, but I'm easily driven berserk (I used to be a copy editor). I wonder if some of them read particularly archaic literature, or were originally German speakers. Or perhaps it's that English grammar rules are byzantine and confusing, and only those of us with weirdly compartmentalized brains can remember them.

I think you're right about A.A. Milne (that's how I use random capitalization) but that's not all of it.

I think random capitalization is influenced more by techno-speak than latent Deutsch tendencies. A lot of common words start out as proper nouns (World Wide Web, Internet) before morphing into common nouns. Much as the use of "web" describing something that does not have flies on it bothers me, I've had to accept it as the new standard.

People who see the capitalization of words they think of as common nouns and don't see the pattern could end up scattering Capital words throughout their Sentences without really considering Why.

"Sometimes it appears to be used for emphasis, like they're using capitalization in place of bold or italics. Sometimes they seem to capitalize all nouns"

I think these are two separate things. I've noticed some writers in The Stranger (I want to say Lindy West and Wm.™ Steven Humphrey, but I can't find any examples.) capitalizing for emphasis. This usage seems to match your A.A. Milne example, but with a more sarcastic edge. It lets a writer borrow the self-important tone of headlines and signage for comic effect. It may also play on the practice of capitalizing nouns that refer to the entire class of things, rather than to specific instances, when saying pompous things like "what a piece of work is Man". (I stole this example from Wikipedia.)

I can't remember any examples of the second type, where people capitalize all nouns. Wikipedia says that this was standard in 18th century English, and was done in the U.S. Constitution, so you might be right that there are versions of the Bible with all the nouns capitalized.

The switch from hand-written or typed messages to ASCII-only email and texts has made people find new ways of emphasizing things. People had to find ways, like emoticons, to work around the limitations of plain text. Even now, a writer can't use typography, even bold or italics, to create tone and expect those effects to survive in all the contexts where their work will end up.