Adsense makes up a minority of Google's ad profits. The billion dollar business is in Adwords, not Adsense.
Right now the problem is getting people to believe in Facebook's revenue to get some confidence back in the market.
Not saying it's is a silver bullet by any means.
From wikipedia [1]:
In Q1 2011, Google earned US$2.43 billion ($9.71 billion annualized),
or 28% of total revenue, through Google AdSense