As I explained in another thread about their toolbar fucking up:
http://www.gofuckyourself.com/showth...hreadid=131896
It tracks where surfers go and creates a top list from it. It is known to be biased towards the companies associated with it and many other things. One example is that only certain types of surfers will ever install a third party toolbar. Another example is if you are the sole visitor to your homepage, and you have an Alexa toolbar installed, then you are representing more than just one Internet surfer; you are representing the amount of Alexa toolbar users divided by the amount of surfers on the net. This means your hompage will be ranked higher than normal. This is why the rankings are only accurate for sites ranked 100,000th and below, due to greater volume of traffic and thus greater accurate of ranking.
I think GFY and webmaster sites in general will be ranked higher than they should, as webmasters are not "normal" surfers, and thus are much more likely to install the toobar, to receive stats on other webmaster's sites, just like I have.