londrum - 7:31 pm on Jun 7, 2011 (gmt 0)
chrism, maybe its got nothing to do with the actual design of the page. if you've moved the ad code to the top of the HTML then perhaps google is just getting more data from that page now.
people might have been bailing out before the adsense code fired (maybe because of some other slow loading stuff that you had above the ad code), but now its near the top of the HTML its firing a lot more. so google is getting more data from that page... and they think that the page is more popular. hence it rises a few places in the SERPs.