As of 5am 13th June 2009 Facebook now lets you register a unique username with your account.
For example if you want to direct someone to your facebook page all you have to do now is give them this link: facebook.com/username
So if you use facebook and would like to take advantage of a unique username, you can do so via the below link.
This is first come first served so be quick if you want your real name or a nickname you often use.
www.facebook.com/username