Google and Facebook are in big competition in this sector. 2009 will be the first year you really see it deployed in big ways.
The issue I see with this technology is that (1) Google really drives search results so marketing probably won't benefit from this & (2) tons of your info. becomes publicly available that perhaps you didn't want your friends knowing before. I'd lean to the google solution if I was a developer trying to increase my rankings in search results :)