I just upgraded to 3.5.1. After the upgrade, I clicked to save a post, and it hung for a while, showing the spinner. The next time I went to my Dashboard, all my posts and pages had been deleted. Comments remained.
I have a backup, so it's not a huge deal. But in my six years of using WordPress, this has never happened. I just wanted to alert the WordPress dev team so they can know that this latest update has a serious problem.