Did some peeking on the wayback machine... domain names that were registered before facebook launched:
flybook.com
sportsbook.com
buybook.com
computerbook.com
skybook.com
Perhaps the most damning, though.... Buddybook.com.. this is from way back in 1999:
"Welcome to Buddy Book.com, an innovative internet address book which helps keep track of all your online experiences."
http://web.archive.org/web/19991128035308/http://buddybook.com/
It's not that similar to facebook, true... but it's a 'social' thing, which by their own logic, seems to be close enough... whoever owns that site ought to sue them!
I'm calling bullshit on that... it uses the same fonts in many places, the graphic for the bar on the side is identical, pixel for pixel, as is the sprite for the clouds, among other things. And if you actually follow the link and RTFA, you'll see that there are several resources in the olympic edition that PROVE the link, including the splash screen for an earlier game made by the same person that he forgot to remove when he re-used the engine.