Interesting thoughts.
In my experience ... Alexa is an inexact measurement ... but not worthless.
Alexa does have all sorts of bias - US centric, webmaster centric, but with their AOL tie-in it's more than just those groups.
Anything below about 200,000 is a reflection of at least SOME human traffic, and below 100,000 a reasonable indication of traffic volumes.
For what it's worth ... I'd use ALEXA ahead of
PR when evaluating the traffic factors of a potential exchange site.
Probably the most improtant reason why ALEXA rankings are valid is that advertsiers pay attention to them - and you can certainly charge more when you're in the top 50K of world sites.
