How effective are the ads on social networks?

As it stands, Facebook does not know all that much about us, and the ads that we are shown are not relevant as a result. The jury is still out on whether social networks can get big via highly targeted advertising. Early trials have shown that CPC is not a likely route and CPM plays are just not as interesting. Yet, Facebook is certainly very aggressively pushing for monetization, likely in preparation for a future IPO. Will they be able to turn it all around and re-invent contextual advertising? The company is full of brilliant people so it's certainly possible, but so far it does not look impressive.