Because I'm crazy, and was a little bored (my wife went to bed far too early for me...), I went ahead and installed the 2.0.1 update from the file in this post:
I did this AFTER rooting using the rooted update.zip file distributed today.
It works, apparently flawlessly. Please read the entire thread and understand what you may be getting yourself into before trying this. If you have any fear (or attachment to 500€ phones that might turn into bricks), you should probably hold off. Definitely don't blame either me or Poseidon if something goes wrong.
The technical details:
Version de micrologiciel: 2.0.1
Version de bande de base: 3GSMEPU91A_U_91.08.15I
Version de la bande de base: UCASHLSEMEAB1B803F.0R
Version de noyau: 2.6.29-omap1 a21146@ca25rhe54 #1
Numéro de build: SHOLS_U2_01.15.0
The home screen is a thousand times smoother, the notification and apps drawers slide instead of bouncing.
No browser problems that I could find - it is fast and clean, and much smoother than 2.0. It automatically reformats text to the screen width when you rotate, and double-tap to zoom worked perfectly on 14 of 15 sites that I tried. The one where it didn't also confused my 3rd gen iPod touch.
All of the 2.1 stuff that I had installed still works. I have not tried the launcher yet (nor am I sure that I will).
Google Nav works in the APK I had installed while still on 2.0, I think.
All of the apps are still in the market. I still get French commentary and French-only apps, like SFR TV and FreeWifi still show up on top of my communications catagory (that's where I live), so using that Italian file doesn't seem to have screwed up my location. I'll test when I get something interesting to test.
The only thing that doesn't seem to work for me now is Voice Search. It can't connect to Google. I'll remove and reinstall and see if that fixes it.
The Superuser Whitelist application is still on the phone and still works, but I don't have any rooted apps, so I can't tell if they work or not. If someone wants me to test one, just point me in the right direction and I will do it.
EDIT: I installed two different terminal emulators. Running su causes the phone to ask if I want to whitelist the terminal app for superuser privs, and if I say yes, the application is added to the list, BUT su does not change me to root (no # prompt). So following my example will lose your root.
Swype still works. Facebook with contact sync works. I took a US APK for that, so I'm not sure if this is a new version or not. Twidroid, Gmail, GTalk, Qik, NewsRob, LeMonde, Astrid, blah blah blah all seem to work perfectly.