go to www.facebook.com/username and register your desired username from there 

Got firstname.surname
Not too bothered really...
so who wants to buy overclockers then? or what have you got to swap with?
www.facebook.com/hirst
"Jason" had already gone to a Facebook member of staff, and the lying cheating sods have also dished out usernames to people less than 5 characters to FB staff too.
O well, no big deal, all a bit of fun!
wow some people actually got up at 5am :s
Argh, all the ones I wanted are gone.
even firstname.surname is taken as well as first initial surname
I was up at 6.15, but couldn't find where to set it and had to go to work.
grrr