Alexa claims to have 10 million downloads, but I can't imagine that the "active Alexa toolbars" are anywhere near that number. Does anybody have any idea what the real number would be? And how high would that number have to be to yield decent apple to apple comparisons for websites? I know the pure numbers are off bigtime, but Alexa seems to be the only way I can get any kind of data that will compare the popularity of sites. And then again I know some people think that the comparisons are pretty useless. But even if they had only 1 or 2 million active toolbars, shouldn't that be enough to get a fairly representative sample?
They were also using the browser stats for a few UK ISPs. Personally I don't consider alexa data to be worth reviewing.