Rand Fishkin has put together a whole bunch of analytical data from some of the top search bloggers. He asked a couple dozen SEM bloggers to share their visitor data and then compared it with external services such as Alexa and Hitwise.
Based on the evidence we’ve gathered here, it’s safe to say that no external metric, traffic prediction service or ranking system available on the web today provides any accuracy when compared with real numbers.
If you want to learn more about where the top search bloggers get their traffic, check out the study.
PS. I had to turn down the offer to participate as when I left FI, I had to start a new Google Analytics account and didn’t have enough data.