Do you use twitter? Millions do. If your trademark is being used as a username by someone else, you may have the right to get it back. The process is relatively simple and quick — last week our firm successfully recovered a username for a client that had been reserved by a competitor.
The rules from Twitter: http://help.twitter.com/forums/26257/entries/18370
My twitter feed: http://twitter.com/tm4smallbiz
Do you have a presence on web 2.0 and social networking sites? Even if you do not, it is likely a good idea to reserve key usernames just to keep others from getting them. And if you do have a presence, have you incorporated your trademarks and made sure others are not abusing them with usernames they have no rights to?
TIP: here is a great tool to search the availability of usernames on the most popular sites: http://knowem.com/