Facebook paid $8.5m to buy the url fb.com

"How much money did Facebook fork over when it acquired Fb.com last year? A cool $8.5 million, more than 42 times the amount the company originally paid for Facebook.com.
In November, it was revealed that Facebook was launching a revamped version of Messages. It combined SMS, messaging, chat and e-mail into one interface, although Mark Zuckerberg repeatedly iterated that, “It’s not e-mail.”
One feature of the new Facebook Messages is that it assigns you a personalized Facebook.com e-mail address. If a friend sends a message to your Facebook e-mail, you will receive it in your Facebook Inbox. Unfortunately, Facebook’s employees were using the Facebook.com domain for their e-mails already, so they had to switch to another domain, which is why Facebook needed to buy Fb.com in the first place.
Facebook acquired the domain sometime last year from the American Farm Bureau Federation, which uses fb.org as its primary domain. At its annual meeting in Atlanta, the non-profit revealed that it earned $8.5 million on the sale of fb.com, according to Reuters."

Source:  Mashable, 12th January 2011