Since last year, Facebook has opened up the "user profile" to advertisers so that companies can target you with ads that are based on information that you share. One example I've seen of this: a sidebar ad with the headline "Calling all CS majors" -- an ad for some IT recruiting site, I think. At first I was surprised (how did they know I studied comp sci?), until I realized that my education history is in my profile. It's like being impressed when everyone seems to know your name and then remembering: oh yeah, I'm wearing a name tag.
I recently read this article about a user who saw his doppleganger featured in an ad that seems to have analyzed his profile photo. There is more than one angle to this coincidence -- the service advertised is Like.com, which uses an image-based search technology like the one you would have to employ in order to generate photo-relevant ads.
However, I still consider it a coincidence. At least I did, until I saw this Man vs. Nature ad on my Facebook profile last night.