[nirav]

Not so much into stats but isn't a good statistical sampling has to have a uniform distribution over population space like strata/demographics?

I wonder what their sample size is for 1.56 billion internet users (http://www.wolframalpha.com/input/?i=total+internet+users).

As a side note: Alexa is an Amazon.com company!, when did that happen?

[bbatsell]

1999. If I recall correctly, it was one of their first acquisitions. It didn't make sense to me then, either.