So far with Win 7 Ultimate, Office 2007: my Outlook crashed one time. I think it was due to the indexing or something. It seems to be running smooth now.
I also installed Call Of Duty 4 and I'm actually getting ok performance out of it. I tweaked the game to get my 250 FPS with no problems. I did have a hard time finding the files to be tweaked due to Windows 7 (like Vista) stores them in a different location that is hidden. The only thing I'm lacking atm is my networked multi-function HP printer. The laser printer connected straight to the computer was installed when I installed the OS.
As for dual boot setup, I made sure that I used another program to partition my hard drive the way I wanted it (I don't like Win7 small system partition). Installed the our BootPro software, copied three files over, added the entry and now I have a dual boot with XP64 JUST in case I run into issues with Win7.
Pretty much everything went seemless. I did experience SLOW downloads tho even tho I have 25 meg (sometimes 55meg) download speed.