europeforvisitors - 3:29 pm on May 14, 2007 (gmt 0)

This sounds a bit like Crystal Ball stuff to me. Taking into account so many anomalies such as time on page, how many pages seen, location, etc. etc. is just too much to expect a 'likelihood of conversion' taking place.

From Google:

We are constantly analyzing data across our network, and if our data shows that a click is less likely to turn into business results (e.g. online sale, registration, phone call, newsletter sign-up), we may reduce the price you pay for that click....We take into account many factors such as what keywords or concepts triggered the ad, as well as the type of site on which the ad was served.

More at:

https://adwords.google.com/select/news/sa_mar04.html