I am completely ignorant about Facebooks ad platform, but if they are just going to target the user, and not the onpage content, then I am not sure how revolutionary that will be since you can already target and stalk users with beacons and the like.
Do you really want to see dating ads when you are looking for advice on wedding rings? What about dating ads while you are looking for cheap antibiotics for your STD?
Mortgage refinance ads when you're declaring bankruptcy etc?
It seems to me that by trying to personalize too much, Facebook runs the risk of missing context, whereas with Adsense, the context is exactly what they target.
FB + Domain targeting would be pretty killer though.
I'm not sure what bothers me more about Facebook. How creepy it is that people willingly allow themselves to be tracked so freely, or that people think that FB is destined to be even more ubiquitous.