When it comes to referrals Google is still the absolute king (at least on this site).
The following chart shows the percentage of visitors that I received by location for all of last year.
At 62% Google generates, by far, the most traffic. Those young pretenders to the throne Twitter, Facebook and even linkedin barely register on the radar, I get more traffic from all of the people using an RSS reader:
Is there any wonder people give so much attention to their Google ranking!