50% of Ad Clicks, 6% of Visitors

Performance of Pay-Per-Click has been a never ending debate.  I just saw an interesting study by Comscore and a few others showing that those who account for most of the clicks are in fact a small percentage of visitors, and they belong to a demographics that usually do not buy:  50% of ad clicks are done by only 6% of the surfers, and the household income of these surfers are less than 40K.

These studies are usually not there as a complete proof of anything, but the finding is interesting rgardless.