From a recent blog post:
“How are ads ranked at Google? Traditionally, it has been the ad’s clickthrough rate (CTR) times its cost per click (CPC). Those with the highest resulting score came first. But Google Slightly Changes AdWords Ranking Algorithm from Search Engine Roundtable summarizes a WebmasterWorld thread about a relatively new change (and pretty much unannounced change).”
Find out how the Google Ad Ranking System : was Tweaked at the Search Engine Watch blog.
