On: Earliest still active twitter users

How do you know what your user id is?

http://twitter.com/users/show.xml?screen_name=yegg

so is the very first number your id?

Yes, buttt..... after around 10,000-20,000 (or somewhere around there), they decided that sequential user id's were a bad idea, so most users won't know what user number they actually were.

(As an aside, my ego likes the fact that I am user 5500: http://twitter.com/users/show.xml?screen_name=iseff)