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.
This is obviously in part due to the upgraded hard drive (the one I had previously was about a year and a half old), but there's no way an older hard drive would cause a 20 FPS decline. Given the previous observations, it's safe to say that Windows 7 contributed significantly in increasing my in-raid FPS.
In WoW, all my settings were at their maximum, with the exception of the shadow setting (which was set to one below the max setting -- setting it to the max position after patch 3.1 caused stability and extremely low FPS issues for myself and several others).
How does this rank with other operating systems? I can't really compare it with my Mac that I have, since the hardware is significantly different. My Mac is 21" Intel iMac running a single dual core processor with a substantially less powerful video card. I can get about 40 FPS max with my Mac.
I did however, install the latest version of Ubuntu Linux on my Mac and ran WoW through that. I found I got around 55 FPS on average through the Ubuntu system. It should be noted however, that while my graphics card is supported, I get the distinctive feeling it's not supported entirely. There is some choppiness that shouldn't be there. This could be a result of minor misconfigurations within the Linux system itself, but if there are things misconfigured it's so buried in the configuration files I wasn't able to find it after an hour of poking around.
When I ran WoW on Ubuntu on the same computer I had installed Windows 7 on, I achieved frame rates of around 65 FPS. It should be noted that for the purpose of this article, I had all non-essential services turned off in Linux (no database, web server, etc...). On Windows 7 the default services were more or less the only ones running.
So roughly speaking, WoW runs better in Windows 7 on my systems.
Overall I would highly recommend that anyone who is thinking about reformatting their computer or just wants to take a new OS for a joyride go with Windows 7. It's much more stable than Vista. Generally I would find some way to crash Vista once or twice a day. Windows 7 has yet to crash.
*We should note that while Windows 7 RC is free now, it will eventually expire next year. Please do your research before you install this or any other modifications to your computer system.