Few months ago Facebook released a new service for companies and individuals.They were all allowed to register domain names on Facebook.Moreover,some companies found their trademark names already taken when they have tried to register it.
That's why you should know how to protect your trademark.
One of the first thing you should do is to register your URL anyway,by choosing a different URL than your branded one.
If you are bothered that somebody else have taken tour branded URL you can always write to Facebook,which reserves the right to remove and/or reclaim any username at any time for any reason.

For more details check out : http://www.imediaconnection.com/content/24058.asp