|Quantcast is a powerful and new web measurement tool
with high potential.
Quancast also provides more stats than anybody else and I really enjoyed using their (US) demographics data. Household income or age can be very valuable tools, especially for niche websites and advertisers.
Also the similar audience data can be a great help for SEO and business development efforts. Besides this great new approach, it is sad, that the tool is currently only available for 20,099,109 US websites. Still, they just started about 3 months ago and I believe that this tool is the most advanced free web measurement tool that is currently on the US market. Let's hope that this will incite the established web measurement vendors to improve their services.