Compete released statistics, which I do not see published on their site yet, saying that Facebook is now sending more traffic to major portals such as Yahoo and MSN, than Google sends to those portals. You can read about this at SFGate.com but here is a quote:
According to Web measurement firm Compete Inc., Facebook has passed search-engine giant Google to become the top source for traffic to major portals like Yahoo and MSN, and is among the leaders for other types of sites.
This trend is shifting the way Web site operators approach online marketing, even as Google takes steps to move into the social-media world.
There is a lot of discussion around this report at WebmasterWorld. Some find this really hard to believe and some do not. Some fault MSN's and Yahoo's SEO efforts (no offense to the SEOs there). Here are some quotes from the thread:
How many links have you clicked on that a friend has added into their Facebook status? Not that many I guess. Maybe Yahoo and MSN need to focus more strongly on their own SEO?
Not all traffic is created equal.
In fact I don't even want the looky-loo type of visitor costing me money by clicking just to have a look. An interested buyer who's taking the time to search for something on the other hand, yes please.
Compete let's you compare traffic of sites, here is an embedded chart comparing visitors to Google and Facebook. Look at the growth:
Personally, I still think Google will dominate the traffic to most sites. The major portals have more "real time" content that is privy to Facebook clicks. But most web sites depend more on Google for less real time content - not that Google does not handle real time content - but you get my point.
Forum discussion at WebmasterWorld.