Matt Cutts confirmed today that the AdSense mediapartners bot (aka mediabot) is indexing pages for use in the Big Daddy Google index. Both Greg Boser and myself have found evidence of mediabot's crawls for AdSense ad targeting purposes have ended up being used in the natural Google search results.

It could definitely be used as a tool to detect when content is being cloaked for either the Google or AdSense bot, particularly since the mediapartners bot has been indexing pages since at least the beginning of February.

It will be interesting to see if other consequences arise for webmasters, such as excluding pages for googlebot via robots.txt that end up being indexed via the mediabot.

If you think about it... this isn't very cool. Googlebot is a well-known robot that people may have reason to block from certain content. It is easy and well-documented how to do this. It seems reasonable that Google should launch a second bot under a new name for a different index and different function. But it seems shady (although logical) for that bot to also feed into the Googlebot index, unless it were to respect robot.txt directives for Googlebot as well as mediabot in those cases. Which I doubt.

Matt Cutts confirms AdSense media bot in natural search index - JenSense.com