Hmmm ... lots of people want it, but I think Facebook's new advertising platform is likely to be a mis-step. A social-utility is NOT a media company. Nor is it an Ad-market.
Of course, Facebook still have to figure out how to get paid, but advertising is going to drive them into thinking that they are one of these preceding categories.
But no succesful web company has succeeded by thinking it's a media company. That's what destroyed AOL and has Yahoo in deep trouble.
Google showed that you can be phenomenally successful as an Ad-Market. But too many companies (particularly Microsoft it seems) took the wrong lesson. The lesson of Google is not that "Adverts are a great business to be in". The lesson is that "disrupting big inefficient value-chains by the clever marshalling of new technologies and new ideas, is a great business to be in".
(Aside : Umair is good on a parallel theme.)
Now, I still think that the opportunity for Facebook (or similar social platform) is to grab a large piece of the market for modelling organizational structure and "wiring people together" which is currently scattered through all kinds of large, inelegant, enterprisey dinosaurs that cost billions to buy and maintain. That's a disruption on a grand scale with commensurate rewards.
OTOH, if Facebook thinks it's going up against Google and Microsoft as an Ad-market, or MySpace and YouTube as a media company, then it's picked the wrong battle; one where it has little disruptive capacity. Any sustaining innovation it can offer in these fields (more relevant adverts through deeper demographic knowledge) can be quickly copied by Google (who are, anyway, pushing to commoditize the whole sector of social networks qua media markets)
Google playing catch-up with Facebook as widget hosting is not a threat to Facebook. Facebook trying to play catch-up with Google as an ad-network is possibly a self-inflicted defeat.