I started Firefox in safe-mode and now my WordPress editor is working fine. Methinks, maybe Google Gears was fecking up the editor somehow. Uninstalling Google Gears, exiting FF, restart in normal mode and see if my hypthosis is valid.

Yup, that might have been it. Some weird caching issues (even after clearing out the regular cache) or Google Gears was out of sync, and woudn’t sync properly, with the upgraded version WordPress. I’ll reinstall Google Gears at some point in the future and see what happens