I have four websites working with WP. To all of them the upgrade to WP 3.5 had been performed on 14th December automatically.
With 3 of 4 websites there were no problems. One became complicated.
There are no differences in server configurations between the sites, pHp 5.4 (sorry, I'm biologist and don't no, what information might be important for the description of the situation).
All websites uses the same 4 plugins: Change Memory Limit, Google Analytics, WordPress importer, WP-optimize. All plugins are up-to-date.
Differences and results after WP upgrade (URL - theme - result)
bonsaivilnius.lt - Suffusion ver 4.4.3 - Everything OK afer update
jonasmackonis.lt - Sundance ver 1.1 - OK
tvenkinukas.lt - Esplanade ver 1.0.9 - OK
musekautas.lt - Arjuna X ver 1.7.1 - PROBLEMS
The problems are with writing the new posts. I couldn't add the picture here to the forum, so there is the link of the screenshot at the picasa storage. At the screenshot I marked all the not-working places with red circles:
1. Not possible add pictures to the post
2. Not possible add tags to the post
3. Not possible change some screen options of the admin panel
4. Not possible turn HTML editor
AND 5. Not possible the automatic upgrade to english 3.5 vertion
The same situation with different browsers: IE, Mozilla, Chrome, Opera (versions are up-to-date).
After the unsuccessful automatic upgrade I upgraded WP for musekautas.lt manually following the instructions. The result is the same.