The site also has a form that trademark owners can submit to try to prevent others from submitting usernames that incorporate a trademark. (See this article from Tresa Baldas at the National Law Journal for more details.) This process appears to be intended for use by owners of federal trademark registrations, as the form requires a registration number. However at least some users have been able to submit the form by putting "N/A" where it requests the registration number.
I haven't found anything from Facebook indicating how they will deal with requests from users who don't own a federal registration. But since trademark rights arise from use and not registration, it makes sense to go through this process for anyone who has been using a trademark and is concerned about someone else trying to incorporate that mark in a username.
Facebook also has a form for submitting claims of trademark infringement or other intellectual property issues. I bet that form is going to be a popular one on Monday morning.
