This is quite the annoyance.
I upgraded to 3.5 this evening and set out to do a blog post, only to find that I could only do a text post. All the helpful items accessible through the normal visual tab I use (like hyperlinks, bold/italic text, etc.) aren't accessible.
I have nine active plugins: Akismet, Polldaddy Polls and Ratings, Share Buttons, Subscribe Me, Text Link Ads, Twitter Widget Pro, WordPress Automatic Upgrade, WordPress Database Backup, and WordPress Facebook Like Plugin. In reading the forums I've seen that a couple plugins have had issues but I deactivated all of them and it didn't help.
I upgraded through the Automatic Upgrade Plugin from 3.4.2, the upgrade seemed to work more or less properly.
The front end of my site (monoblogue.us) looks fine, and aside from the big inconvenience of not having the visual box the back end seems okay as well.