I'm sure this has already been considered by the Adsense team, but the improvement in targeting would be so significant for many visitors to my sites, that I think it's at least worth a mention: the Adsense script should parse the URL referral string for keywords if the visitor came to the page directly from a search engine and use them as one of the inputs to the algorithm that dynamically chooses ads that are shown. Adsense's javascript has access to the referrer and it passes it to the program that picks ads, but it doesn't appear to be currently used in ad targeting. Yahoo's Publisher Network doesn't seem to do it either (could there be some patent issues involved)? Parsing for keywords from most search engines is not difficult (Urchin does it...)
