I use Adsense Insert 1.4.4 by Naeem to intelligently insert ads into my blog. When Jetpack is active, all of the ads float to top of my theme "Twenty Eleven." When Jetpack is made inactive, expected behavior resumes.
I tried deactivating all the plugins that I had installed in the last 3 days and those that had just updated to rule them out. It was only when deactivating Jetpack that I could restore the normal behavior.