In fact, social content is hard to monetize due to privacy concerns, thus IMHO Facebook is lacking of a clear long-term business model other than advertising. Google's investment in Zynga doesn't help that much either.
They have taken the right path targeting developers but I don't seem to understand where that is going.
So my answer is no, I wouldn't buy Facebook stock, except for speculation purposes.
Facebook barely scratched the surface of the advertising potential so far - targeted paid ads in streams, a recommendation engine and beating Foursquare et al at the location game are all feasible and likely to be more lucrative than their current rather passive sidebar ads.