http://www.sitepronews.com/2008/04/25/google-previous-query-reason-for-crazy-google-rankings/
I reference Google's personalization of Search quite frequently in my Search Engine Training Classes. One of my favorite live examples is to do some searching on "Bugaboo Strollers". This is a very expensive item, so the correlating CPCs are also high. Then I will do a search on something like "Baby Diapers", and very frequently Google Adwords will display a Bugaboo stroller ad. I think it is very impressive. I think it is a practice that not many people are familiar with. The article above delves into the topic even further and how it is being used in natural search.
