Google Adsense google_hints Code
It had come to the attention of a few people that some adsense blocks on some websites contain a section of code like this google_hints="your,keywords,go,here"; , Some discussion was sparked by this, Then a moderator Vangogh had the idea to email google and ask them about this, Best to get it from the horses mouth.
Googles response to the google_hints adsense code question was
Thanks for your inquiry. The feature you're referring to is one of several features the Google AdSense team is currently testing for a very limited number of publishers. At this time, we are not able to offer these features to other publishers. Should we offer these features to additional publishers in the future, we will be sure to notify you at that time. I appreciate your understanding.
It looks to me like they are still beta testing the google_hints code.
personally i don't know if this is a good idea. Adsense is supposed to be contextual, Meaning the adsense bot visits your site, reads the page, and then gives you adverts based around your content, The google_hints adsense code will effectively mean publishers can choose what adverts are being displayed. So if you are currently publishing content that produces adverts that pay 5 cents per click you would be likely to just stick the keywords "asbestos, mesothelioma, cancer, lawyer, compensation" in the google_hints and hope for those elusive $40 clicks. It would mean less clicks, But should mean more earnings.
I believe to make this available to everyone would be a huge mistake by google.