Im currently running Windows 7 on a new system I built as a Christmas present
I never used Vista as I found it to be very annoying and frustrating. I'm running Windows 7 Professional 64bit edition and I have been really enjoying the new system. The speed is great, my i7 CPU never seems to be too stressed. It handles new hardware great and I haven't had any problems with it so far.
The new interface is great, runs smoothly and multiple monitors are a must for windows 7
Very impressed with Microsoft's effort.