How on earth does it get its information?
Alexa, Quantcast and Compete all use panel methodology to estimate web traffic across all web sites. With Alexa it’s a “toolbar” embedded into a browser a la Google destop and toobar. The toolbar reports your browsing and an algorhthm uses your behavior to extrapolate what other “yous” are interested in seeing and doing on the Internet. As with anything, the methodology is limited by imprecise or biased samples (note: I’m not indicating any intentional bias or skew).
These traffic sites are better for sites with wide reach and appeal (Yahoo, MTV, weather.com and yes Drudge) whereas they lose accuracy when estimating sites with regional or niche appeal.
A nice comparative tool but not always 100% accurate. I have one site in my portfolio with nearly a million visits a year that gets reported at 1/2 the actual traffic on the Quantcast, Compete, Alexa sites. My numbers are good but theirs are limited because they rely on estimates.
http://www.quantcast.com/docs/team
This "new user" has put up at least three threads on FR promotiing other sites. At least two are back by left-wing progressives.
http://www.freerepublic.com/tag/by:nycfearsome/index?brevity=full;tab=comments
I am taking all of those sites with a very large grain of salt.
Also note that they can data-mine users, caveat emptor.