I often wonder about this since I believe Google pulls traffic stats for a site based upon Adsense impressions. Is this data available to volume Google advertisers or subscribers of Google analytics?
If so the problem with Google doing this is what about sites that only occassionally display Adsense Ads and additionally only put them on pages deep within the site.
This would give Google and companies using their data the false impression that the site sees little traffic. Therefore is it best in these cases not to use Adsense at all in this manner or use it consistently across all pages and on the home page.
If you think Google is restricted in seeing a site's traffic to adsense impressions then you're missing a whole heap! How about: - toolbar users. Particularly those with reporting turned on... sending all that data on the pages they go to back to the mother ship - google analytics. Not just for the site its installed on - Google will know about what sites send traffic to them, too. If site X sends lots of traffic to a site with analytics then obviously site X has at least that much trafic. - straight search results - sometimes they put click tracking in the search results. I'm sure there are others. Just assume that Google Is Big Brother as far as internet trafic goes :)