Have played WoW on my MBP on numerous occasions at 4-6 hour stints. Along with lots of video encoding and other high useage requirements over the last year now.
You start ramping up a video card and the fans are going to throttle up. This is normal, don't worry. Same thing happens in a desktop rig. Typically it won't be sitting a foot from your ear, so it's not as noticeable.
You could get a stand. I went for the
iLap. Works well, as when I am playing, I'm usually sitting in my recliner with the MBP on my lap or occasionally in bed. And it definitely will get too warm to keep it sitting on your lap for hours at a time playing WoW.
Can't say as I agree that using your hardware to it's full potential isn't good for it's longevity. This could be said about anything. Only use a device to half it's potential and it will probably last longer than using it to it's full potential. This statement could be made about a shovel.
There is the thought that if you're purchasing a rig primarily for gaming, get a desktop, and I agree. However, I would not agree with diminishing the useage of your machine simply because it is a notebook. The MacBook Pro has either been designed to be able to use the hardware or it hasn't. I prefer to take the former view. If I can't use the hardware, then might as well have gotten the MacBook and saved myself $1500.
Just as a side note: Have a P4 3.4 that has been running at 3.9Ghz for 4 years come Feb. (and on air) with a video card that's overclocked by 100Mhz and going into it's 2nd year. The CPU has hundreds of hours running at 100%. Am a firm believer in using to it's fullest whatever hardware, equipment, tools, etc. that I have paid my hard earned $$ for.