
A great tool and a new layer to Google Trends. With Google Trends for Websites users can check and compare traffic data for different Web sites, including their competitors. Much more accurate than Alexa.
Now, the advertisers have the most powerful tool to check the publisher sites before starting an ad campaign.
Google Trends for Websites provides simultaneously traffic stats for up to five Web sites with bar graphs and charts, popularity in different regions, estimate of unique visitors, etc.
Google Blog consider it "a fun tool that gives you a view of how popular your favorite websites are, including your own! It also compares and ranks site visitation across geographies, and related websites and searches."
Most interesting, for a google.com search the answer is "Your websites - google.com - do not have data to display."