I'm going to suggest that Facebook's ad potential is probably higher than the current capabilities of AdSense, which are a huge moneymaker for Google. Facebook has the technology, data, and reach to push out ads that are better than Google's AdSense ads because they will be user-oriented instead of content-oriented. My belief is that media sites are far more likely to generate clicks from Facebook driven ads because the content of those sites is generally uncorrelated with "intent". Like how candied cereal commercials are aired during children's cartoons. Nothing in the context of a cartoon indicates that Froot Loops should be advertised (unless the cartoon stars an enthusiastic toucan), but everyone knows that it's a really good idea.
Now I have noticed that many AdSense ads are starting to "follow me around". e.g. I was evaluating some software and for the next there days I kept seeing banner ads for that software, even here on CoBF. Pretty cool. A little creepy but I have accepted it as a fact of the future.
No position in Facebook but I love when a stock gets hammered for this reason. I might dip my toe in if it gets really ugly.