Installed WP 3.5 and don't seem to have any problems except for when I install most plugins. Seems like most plugins generate errors of Undefined Variables and/or Index issues.
It's not all plugins, but most. Even ones that are tested to WP 3.5.
I am noticing the problem in WP-ADMIN pages as well as public content pages.
These might be harmless errors that should only be displaying when PHP Debug reporting is turned on. I am on a Windows server but my WP 3.4.2 sites don't have this problem.
I've completely reinstalled WP 3.5. Also performed a fresh install of the theme I use.