Jeremy made some big news with a post at his blog named Matt Cutts Confirms Media Bot Crawling For Big Daddy. In response to that, Matt Cutts commented at his own blog saying;
It's literally just a crawl cache, so if e.g. our news crawl fetched a page and then Googlebot wanted the same page, we'd retrieve the page from the crawl cache. But there's no boost at all in rankings if you're in AdSense or Google News. You don’t get any more pages crawled either.
Danny and Jennifer dug deeper into this. Danny explained;
In other words, there are two big issues with the AdSense crawler helping Googlebot:
(1) Since the AdSense crawler swoops in fast, it could be a way for people to effectively get fast inclusion of their pages. Just add AdSense, wait for the AdSense bot to fly in, and you're set. (2) Is having the AdSense crawler likely to get you a RANKING boost, in addition to getting INDEXED faster. I've capitalized both words to stress them, as a reminder that being in the index isn't the same as ranking well for a query.
Matt's saying that no to both cases. There is no ranking boost. As for fast indexing, no to that as well. The AdSense bot is simply refreshing the cached copy of your page -- but the copy in the index, what people are searching on, won't be updated.
Danny then explains that this causes an other issue. The new issue is that Google may show a fresher copy of a page that is in the index, that it actually used to rank the page. For example, Googlebot crawls and page, put that page in the Google index. That content is what is shown in the Google Cache and what is used, in part, for ranking purposes. Now if they use Google AdSense's Mediabot for the Google cache, the cache may most likely be more up-to-date than GoogleBot. So your Google cache information is more likely more up to date then the index the searcher searched on.
Forum discussion at WebmasterWorld.