Q. What's a Premium Username?
A. Choosing your bitcoinwallet.com username is like registering a valuable domain name that you're proud to keep forever. On most sites the assignment of usernames is a land rush: first come first serve. To prevent ingenius early adopters (bless their hearts!) from registering all the best usernames in the first 5 minutes we've added some friction to give everyone a chance at getting their desired username. The pricing for Premium Usernames is based on the length of the username and whether it contains numbers. Usernames with 1-4 characters (X, Bo, Jon, Bill) are Premium Usernames. Usernames with five or more are free.
1 character names = 2 btc + .2 btc per year
2 character names = 1 btc + .1 btc per year
3 character names = .4 btc + .04 btc per year
4 character names = .1 btc + .01 btc per year
5+ character names = Free
Seems the better addresses on there are reserved as premium names you have to pay for.