Findings:

printable version

Here's the stuff we found when you searched for "usernames"

username clashes (user)
username (user)
username:) (user)
Advice on Choosing a Username
new username (user)
I am Jack's username (user)
the "username taken" bug (collaboration)

If you Log in you could create a "usernames" node. If you don't already have an account, you can Create A New User...