I have a pre-Unibody Macbook Pro that has served loyally and well for some time - it's one of the 15 inch Core 2 Duo models with an Nvidia GeForce 8600M GT graphics card.
While using it today, it suffered from what could best be referred to as a "stroke". Running in Bootcamp playing World of Tanks while on battery power, it suddenly powered off and then restarted. The battery was not empty at the time, and I assumed it was heat related and let it stay off.
I later restarted the machine, and had the same problem - almost instantly after launching World of Tanks it powers down and resets, although it seems to tolerate plenty of internet surfing and other non-GPU based activity. I also noticed at the time that the battery indicator is at 58% and not charging though it is plugged in.
Making sure this wasn't a Windows issue, I restarted into the OS X side of things after letting the laptop cool down for about an hour and a half. Again, worked fine using the internet and other non-GPU tasks, tolerated playing World of Warcraft for awhile (though the fans made it sounds like a jet) before it powered off. Same thing with the battery - it says it's fine, its getting power from the AC adaptor, but the battery isn't charging. During these tests, the battery lost ~1% charge.
I also believe that unplugging the laptop will immediately power it off, despite the battery claiming to have 57% charge, though obviously I'm not going to test that while writing this.
Any idea what's going on? Simple overheating? Battery problem? GPU problem? Multiple problems showing up at the same time?
I've tried resetting the SMC twice, no fix there.
UPDATE: I've done some additional testing - installing a fan controller and temperature measurement utility on the Windows side. With the fans spinning at 6000 RPM, the GPU was only at ~60 C when it shut down, which seems a little low for the "Shut down to prevent catastrophic failure from over heating" answer to the problem.