Well, I bit the bullet and upgraded my Vista SP2 x64 system that was an old bloated build from last year. It took over an hour and a half.
I had no real issues, except it seemed to have messed up my profile with my settings, but I logged off and it seemed to have fixed it. After the first boot when you sign in, it was fine. I then installed the Nvidia and Creative drivers and restarted, it was then, as it was logging me in I heard an error sound and when it logged in, everything was default and it said it was unable to find the profile and it showed some path. Aero wasn't even on, it was in the Windows 2000 UI. Weird. I logged off and back on and everything was back (icons, Aero, etc).
My system scored a 5.9, same as before, but this time the 5.9 was in my HD only, the rest was 7.3 for Proc and RAM (Q9650 and 4GB) and 6.4 for Aero/Games (G200). Highest cap is 7.9 this time.
There were a few Windows Updates, mainly for IE8.
Seems to boot up and shut down faster, but not by much. Overall, it feels snappier. Games seem to run the same. My memory usage is lower and my processes are about 10 less than I had in Vista x64 SP2. I didn't do a clean install because I am going to do that when it's RTM and I didn't want to do it twice.
I am now comfortable knowing my system is supported and runs Windows 7 very well. I can't wait for RTM and then I will do a clean install.