On: Tipjoy: Why Didn't it Take Off? Pathology of a Floundering Web 2.0 Startup

[abstractbill]

They're all wrong, in different ways for different sites. I wouldn't trust any of them for more than an order-of-magnitude estimate.

[axod → abstractbill]

I find alexa most acurate for trends, but I agree, all pretty useless.

Quantcast being the exception as you can add some js to your site so they actually measure the figures.