Shoemoney reports in his blog that Matt Cutts has just verified that the AdSense mediabot is performing spidering of content which will also be added into the search results pages.
As you all may know, the AdSense bot will spider a page which has Google Ads on it, so that they can figure out what keyword-targeted ads should be displayed on the page.
Now, this bot will also supply the spidered content over into Google's web content indices, allowing the page's link to appear in the SERPs. Google apparently did this to improve their overall efficiency, so they wouldn't need to spider pages twice.
I think this potentially also creates a new page URL submission method -- add AdSense ads onto your page, and it might get spidered sooner than otherwise.
[edited by: tedster at 6:33 am (utc) on April 20, 2006]