"we're introducing enhancements to our pricing model for advertisers. Google's smart pricing has always provided better placement for better performing ads, and reduced the cost of a click to the least amount possible for an advertiser to stay above their competitor's ad. Now, with the new AdWords pricing model, we’ll also automatically adjust the price of clicks across the Google Network based on their expected value to the advertiser. A number of factors will be taken into account when calculating the expected value, including the keywords or concepts that triggered the ad. For example, a click on an ad for digital cameras on a web page about photography tips may be worth less than a click on the same ad appearing next to a review of digital cameras."
Nuno Oliveira
There are some pretty good links about it in Alternative PPC engines forums.
