"The first 5 or so sites are from 2009, the others date back to 2006 -- but often times Quantcast isn't as accurate as it could be, the same goes for Compete and Alexa. For anyone looking to buy/sell these, you will want access to Google Analytics to verify all true traffic data. I've seen sites that have 1,000,000 uniques that only show 300,000 in Compete." - Andrew Wise