Location data is per-post, I think.

Good luck with the test thread thing, that was substantially weirder than I thought it'd be

edit: also
23:20 < Nortaneous> hm so there's no maximum username length limit and if your username is longer than the post box is wide your posts don't show up at all
23:20 < Nortaneous> but i guess that falls under assume users won't intentionally break shit

(I changed my name to something very long, that's how I noticed the avatar bug)

edit: To try to list what I found over in the test thread:
There's a distinction between original and current username. In the 'most recent' box on the front page, blog posts are displayed as being by #{original_username} and forum posts are displayed as being by #{current_username}.
Avatars are associated with original username, not current username.
I don't quite understand this one, but: say you register an account with the original username foo, and then change it to bar — so its current username is bar. Then you register another account and give it the name foo — it'll go through, sort of, but it'll act weird in the ways I described there: you can't have a profile (even though profiles appear to be associated with current username — if you try to make one, it complains of a collision) or an avatar (nothing shows up at all, not even the default avatar box), but you can edit posts. I'm not sure if you can change your settings and so on — I didn't prod at it much. Anyway, you take the new foo account and change its username to baz, and then its original username becomes baz — and then you can change its (current, but not original) username back to foo, with all the behavior expected from the two points above. (It'll take on the avatar associated with the original username foo and its forum posts [but not its blog posts] will show up as being by foo.)