I got my M600i yesterday and have been using it constantly since. I immediately updated the firmware before I even put in my SIM so I don't know about the original firmware. So far, it's pretty damn nice! It can be a little slow, but only if the application isn't already open. For that reason, I always make sure that the contacts and messaging apps are open. It's plenty fast then. I was used to a 7105 before which could be slow as hell at times so I don't mind so much.
In any case, the phone is very sexy. The screen looks INCREDIBLE and the different applications merge pretty well. UIQ 3 is looking very very nice. Unfortunately, I completely agree with another poster that the one handed operation without a stylus wasn't really completed. It's about 1/3 of the way to where it needs to be. You can't even answer the phone without touching the screen! I've resorted to just touching it with my fingers which is ok but not preferred. When the screen is on though, you can't even see the fingerprints so its not that bad.
Getting Exchange Activesync working was a PITA. SE doesn't include the CA certificates for Equifax or GeoTrust which provide our SSL certificate where I work. I had to find them and install them in order to get ActiveSync working. But now it works great!
Honestly though, how could they not include the capability to view exchange folders? I sort everything into folders almost immediately when I get the messages and now I can't access them at all! It feels like the exchange activesync software is more of a gimmick than anything else. Not fully implemented yet.
The only workaround I can think of is setting up my same account with IMAP and accessing the folders that way. It'll be annoying, but it'll work.
I'm going to use it for a week or so and then post a longer review with pictures. I was a crackberry addict before so I hope to give some insight to the transition.