The installation and configuration of Windows 7 went very smoothly. For the technically inclined, my computer has four gigs of RAM and operates off of two dual-core Intel Core2 processors. I have an nVidia GTX 260 graphics card, which is the latest generation. There's a bunch of other bells and whistles that I have as well, but those are the big things relevant to what I do every day here at WoW.com and how I play WoW.
Prior to installing Windows 7, I used Windows Vista updated to the latest patches. I got about 60 FPS on average, with a maximum of around 100 while idling in some far off place with not a lot of traffic; and a minimum of about 50 while in some of the more graphic intensive raids / battlegrounds. After installing Windows 7 I was running at about 75 FPS average, with a maximum still of around 100. However more importantly my FPS during raids / Wintergrasp shot up to 70.