The short answer is that it depends if you are using your domain name as a trademark.
By Erik J. Heels
First published 3/2/2003; LawLawLaw Newsletter; Clock Tower Law Group
Is your domain name being used to identify the source of the products or services you offer? If your domain name is distinctive and is being used as a trademark, then you may be able to secure federal registration for it. The more fanciful and less descriptive your mark, the more likely it will qualify for federal registration. Apple has nothing inherently to do with computers, Amazon has nothing inherently to do with books, and these are both strong marks. On the other hand, a recent “Non Sequitor” cartoon showed a man from “Mammoth Moving Company” explaining to his customer that “they only move mammoths.” Because that company’s mark is descriptive of what the company does, it would not be able to federally register the mark! One reason you might want to register your domain name as a trademark is to prevent “cybersquatters” from using confusingly similar marks. For about two years, AmaXon.com had its own web site (http://web.archive.org/web/*/http://www.amaxon.com), but now “amaXon.com” is owned by Amazon.com. Finally, if you already have trademarks, you should register them as domain names to protect them from potential future confusion. For more information on this topic, see “Trademark Registration of Internet Domain Names” by the USPTO.
http://www.uspto.gov/web/offices/tac/domain/
http://www.non-sequitur.com/index.php3?inmonth=12&inday=29&inyear=2001