I was always uneasy about the facebook terms of service, which allows them to own and sell any information you put on there.
link
They are injecting ads into personal conversations, so it could be something like 'hey hope you had a good time at the beach...REMEMBER TO BUY MEGACORP SUNBLOCK...tell Jenny I said hi"
Also, remember how they own all your pictures? They are selling them to companies to use in ads:
"For example, if a friend has booked a vacation on Travelocity, the online travel agency will be able to display the friend's photo as part of a "social ad" to entice the user to buy flights and hotel stays. Advertisers can similarly have their pitches appear when friends review restaurants and buy books or DVDs."
Companies are now going to be making facebook pages and advertising based on targetted friend groups.
Etc, etc.