Have you registered your Facebook username yet? If you haven't, good luck securing your preferred name. Over 3 million users registered their Facebook usernames (such as www.facebook.com/david) within hours of the service going live at 9 p.m. PST on Friday night, according to Bloomberg.

Until now, Facebook URLs had been a sequence of random numbers. With the introduction of usernames, however, personal Facebook web address will be a lot easier to remember and to find through search engines like Google.

Due to concerns over cyber-squatting and other privacy/trademark issues, Facebook had allowed certain organizations, fan pages and high-profile users to reserve their preferred username in advance. The rest were given away on a first-come, first-serve basis.

Some Facebook users were not above having a little fun with their vanity URLs, with usernames such as www.facebook.com/error404, www.facebook.com/twitterisbetter and www.facebook.com/rickroll being snapped up early, Mashable reports.