If you're planning on setting up any kind of online community for your business — and who isn't these days? — know that Facebook has begun suing to protect "the distinctive BOOK portion" of its trademark, starting with Teachbook.com.

"If others could freely use ‘generic plus BOOK' marks for online networking services," the company writes in its federal court case against Teachbook, "the suffix BOOK could become a generic term for ‘online community/networking services' or 'social networking services'."

Imagine: Someone ripping off the name of an existing social networking tool for his own site. Why, that hasn't been done since 2004 when some punk kid at Harvard registered TheFacebook.com while college administrators were already developing their own "online facebook." Anyway, BlackBook, the city guide dabbling in online networking and iPhone apps, should watch its back.

[Photo of Facebook CEO Mark Zuckerberg via Getty Images]