Facebook sends more traffic to portals than Google does

"Using a snapshot of Web traffic from December, Compete's director of online media and search, Jessica Ong, found that 15 percent of traffic to major Web portals like Yahoo, MSN and AOL came from Facebook and MySpace. The lion's share of that traffic, 13 percent came from Facebook.
Google, which has profited handsomely from directing Web surfers to their destinations during the past decade, was third with 7 percent, just behind e-commerce site eBay, which had 7.61 percent. MySpace was fourth with just under 2 percent."
Source: Data from Compete.com, reported by SFGate, 15th February 2010
Note: I think that this is US data only