Read their term http://www.facebook.com/legal/terms they are things like "transferable, sub-licensable, royalty-free, worldwide license to use any IP content that you post on or in connection with Facebook"
As Stallman pointed out in the interview, the scale of the monitoring is on a different level of what you can do manually. No matter how hard you try, you will not know what websites pessimizer has visited, FB got a list of his/her visits on any site that contains a like button (doesn't matter if he/she uses FB).
Beside the scale of information disclosed, that's how it can be used or not. I'm pretty sure I can decide what products are endorsed on my blog, not so much on FB, and if we visit pessimizer site, no one will now. On FB, they could use this information to know pessimizer better. Guilty by association ;)
Probably they have some common heuristics to spot a fake, but those cannot be too clever.
Re: Scale of monitoring
Does this not just make the haystack bigger for the same number of needles?