Whenever I go to a new site that requires a signup and use of a username, I usually try to use the same name I use everywhere else. It cuts down on confusion for me, as when I go to a site and need to login, if I always use the same username, I should be just fine.
Unfortunately for me, there is apparently another Susabelle out there (perish the thought). So sometimes I have to resort to a secondary username, smkelmer.
A new service has been launched to tell you if many of the web 2.0 sites you visit already have you listed as a user, or someone with your username, at any rate. Usernamecheck will run through a list of popular (and common) 2.0 sites to see if your name is taken or available. I found out my doppleganger already has registered a twitter account with my usual username. It’s a good thing I didn’t want to have a twitter account.
Now, if I an just keep all my passwords straight, I’d be in good shape. I have yet to find a system that works for me, and I’ve tried quite a few.