If investors were looking for clues as to how Facebook could ever get to the $104 billion valuation it IPO’d at, Facebook Exchange should excite them. It shows Facebook is willing to shift towards slightly more aggressive advertising mechanisms. While just a year ago Facebook ad targeting was only based on user-entered personal information and interests, now both browsing behavior and activity within apps, for example listening to a specific artist on Spotify.
And for users who aren’t abnormally worried about privacy, Exchange means the ads they see could be for things they actually want to buy.
via techcrunch.com
I don't think this is going to turn out well for FB. I could be wrong, of course, but this will be problematic.