If anyone else found that their page tabs (or page lists) were screwed up after upgrading to 2.1, I found that changing my
wp_list_pages('depth=-1... found in my header (zen-min theme)
to a value of 'depth=1... that is, dropping the minus sign
seemed to resolve the problem.
I use this call to generate page tabs at the top of my page, but was using depth=-1 so that sub-pages would not show up. For some reason, after the 2.1 upgrade, all the sub-pages were showing up in my page tabs. Don't know why it works now, but it does.