I've read some threads on Mediapartners bot, but no one went in depth. What does it do after a visit? How long does it take to do it's thing after a visit? How does it interact w/ other parts of Google. Feel free to respond here or send me a sticky.
I don't believe it crawls, but I may be wrong. If the site has already been crawled by normal Google bot, Mediapartners bot will use that data. Its uncertain if mediaparters bot sends data to normal Google Bot.
My own experience is I have seen the media partners bot hit just seconds after a visitor hits the page. This does not happen all the time but very frequently. Make sure the pages are highly targeted with the on-page text. I have seen what seems to be refined ads on the page go to very refined ads after the media partners bot hits.. This is on one of the sites (not in profile of course) I watch that is doing absolutely fantastic (beyond anything I would have expected).
One of my sites is kind of new. I haven't used it for a while other than internal tracking system. A few days ago, i replaced all the contents with new look and files. The new site had "Active Users" tracking with IP addresses for admin.
When I was uploading a few more files after I put the adsense code, I noticed there were a few visitors. Since this site was not used and not completed yet, I was not expecting any visitor yet.
But there were a few visitors following the pages I visited after uploading the contents to check it it looks ok.
I tried to scare off these visitors for twenty minutes by changing file names, etc. not to show my work-in-progress site.
Finally when I typed in the IP address in google.com, I found that those were the Media bots.
I was fighting with bots online...Funny..but real story.
Anyways, I now know that the media bots visit a page if there is a request for adsense from the page.