Facebook has created the ability to have a username. This is different than your email address, and your profile name. No two peoples can have the same username. Once you have created your username, it's easier to refer people to your profile because it's simply: facebook.com/username.
For example, to add me you just type in the URL:
http://facebook.com/tomchurch1 which is consistent with my other internet usernames such as YouTube:
http://youtube.com/tomchurch1
This might seem a bit irrelevant and pointless, but it's much easier to tell a girl "my username is 'bigwilly'" (already taken) than to say "search for 'bigwilly' on Facebook, my profile picture is of a giant penis." In a certain aspect, this move by Facebook has stepped on MySpace turf because now (in case you hadn't notice on the bottom of the log in page) businesses, bands and celebrities can make a special Facebook page. With it's own URL, what's the difference between myspace.com/bigwilly and facebook.com/bigwilly?
Facebook has more users, much more traffic, credibility and value. MySpace recently (as explained on TechCrunch) revealed that it has slumped massively. So get a Facebook username fast because as I experienced they're already running out very quickly.
How Do I Get A Facebook Username Tom?
Once you're logged into Facebook, click Home and there should be a message at the top of the News Feed. That's how I did it. Alternatively use a search engine.