I've noticed for a while now that many people do not know they can set a vanity url for their Facebook Profile Page. Facebook calls it a username. Let's first explain what a Facebook Profile is. A Facebook Profile Page is a personal account on Facebook where you can connect personally with your friends and family. You can see each others status updates, see what your connections are posting on other people's pages, share photos and videos, etc. This is really how friends can share what's going on in their lives.
This is not to be confused with a Fan Page, or what they are now calling a "Like" Page. Fan Pages were created for business entities, places, public figures, etc that could potentially have thousands and thousands of fans or customers. A Fan Page is a way for brands and public figures to communicate with their customers or fans without connecting personally.
A vanity url is where the string of numbers for the Profile or Page is replaced with something you choose. For example, my Fan Page is http://www.facebook.com/charlieprofit (be sure to click the "Like" button) and my Profile is http://www.facebook.com/charlieprofitreport. (You can also "Like" CAB Radio on Facebook at http://www.facebook.com/cabradio). Using vanity urls is useful for branding purposes, or just to make it easy to give out to friends and family. It's much easier to tell someone to find you on Facebook with a vanity url, than to give out a long string of numbers.
How do you set up your vanity url? This is very easy. First make sure you have logged into your Facebook account. Then go to http://www.facebook.com/username. From there the instructions will prompt you to choose your username. It is permanent, so choose wisely. Make sure you do not misspell or make a typo. The process to correct a mistake like that is almost impossible. It would probably be easier to set up a new account, but then your history is not connected with the new account. If you manage any Facebook Pages with more than 25 fans, then you can also set the url for your Fan Page here.
I hope you found this information useful. If you'd like more information on what a username is you can click here: http://www.facebook.com/help/new/?page=897.