"You will not use our copyrights or trademarks (including Facebook, the Facebook and F Logos, FB, Face, Poke, Book and Wall), or any confusingly similar marks, except as expressly permitted by our Brand Usage Guidelines or with our prior written permission."No one is forcing you to use Facebook, of course, and it’s a free service to boot (although with an increasing amount of lucrative advertisement, which is sold on the viewing habits of all those “free” users). Facebook isn’t worried about its users misusing its name or its components – the real gambit with the mandatory user agreement is that it bolsters its legal claim in courts against possible competitors. Basically, the lawyers and other strategists figure might was well test to see how much we can get away with. When the law slaps us down, we’ll retreat a little and recalculate. But it can’t hurt to be aggressive, even presumptuous. And it might really pay off, so why not? According to ArsTechnica, Facebook has 73 active trademarks with the US Patent and Trademark Office: the letter "F," "Face," "FB," the number "0" with a period, "F8," "Facebook Developer Garage," "Wall," "Facepile," "Nextstop.com," "Facebook for good," "Friendfeed," Facebook Insights," "Facebook Pages," and "Facebook Ads." "Book" doesn't appear on the US list yet, and it probably won’t as others have tried unsuccessfully to register “book” with trademark authorities here and abroad. But it doesn’t have to, for while the addition of "book" to the user agreement isn't as strong as a registered trademark or copyright, it covers people who have ever used Facebook – including anyone who might ever want to start their own site with “book” in the name. Pretty clever work-around, no?