WoW works very well
WoW works very well on my new iMac. I've got the 24", 2.8, w/ 4GB of ram. I also play it on the road with my 12" Powerbook 1.5GHz 1.25GB of RAM, and it runs pretty well on that too.
Your frame rates will be different depending on where you are in the game. In Outlands you'll see a significant drop in frame rate, and I'd guess that's because it's got more graphic intense stuff than the older maps.
My 24" sees avg. 25-35 fps in Outlands, and it sees 35-55 fps when not in Outlands. Indoors and outdoors frame rates are different too, but I can't remember those off the top of my head.
I had it freeze 1 time when I switched from full screen to windowed mode in the ~1 month I've had it.
One suggestion though... don't buy your RAM from Apple. You can get a lot more ram for your $$$ if you buy it from a 3rd party like OWC. I've not had any trouble with the 4GB that I bought from them that only cost me about $250 as opposed to the $700ish that Apple is charging. Plus I have a 1GB stick left over that I can sell if I want.
One more thing. With the latest updates Blizzard introduced some Mac Only features, and although they don't work on the Aluminum iMacs right now, Blizzard says they are working to resolve some driver issues to get those features going. The features ahve to do with saving video of what you do in WoW... My guess is like a raid or something like that, that you might want to save a Youtube later...
Good luck and I hope you enjoy. My powerbook had some hiccups when I first got it, but you will greatly appreciate the longevity of a solid computer, aka MAC