Facebook now allows users to personalise their facebook url (web address) by selecting a unique username similar to Twitter.com/thelostagency
This process started at 12:01am (EDT) on Sat 13th June 2009, the system allows you to pick the suggested names or create your owner. If the username is available you just have to click confirm and it is done. The only downside is that you can only have one username and this cannot be reset once selected.
The interesting security feature is that even after an account is removed/closed the username will not be then made available as other services allow. This might produce problems if a spammer creates an account, claims your username and then is closed down, so my advice is to register your username now rather than later, considering how many other people may have your name with 200 million users…
To reduce the landrush and spammers, users names for new users created after this annoucement was made public will only be made available after 28th June 2009.
Facebook can also reserve the right to remove or reclaim any username at anytime for any reason. The caveat is if you have a name in common with someone famous or important they may steal your name in the future if it suits them under this broad T&Cs. Read more about the Facebook username process.
Update: It is almost time to open up the landrush for usernames for all new accounts created since 9th June.