He, I don't know everything either, but this is what I know;
You can get your pc (windows pc, with a bios) faster by clocking it over, so more electrones going through the CPU in the same time. This makes your CPU really hot, so you need cooling. (this was actually useless information, but whatever). If it get's too hot it will damage your pc. Just like you can't handle 100 degrees
celsius. The heat will probably smelt things (don't know this for sure), but what happened to my old pc was that the motherboard got hot, and then cooled down, hot, cold etc. This expansion all the time cracked the board and damaged it, so we had to replace it (with a nice mac that is).
So when it get's too hot it will damage things, and it will wear faster. So computer lives shorter. That's why
when overclocking people cool there pc's.
But your mac isn't overclocking or whatever, it just get's hot when it needs to do a lot. And apple had 2 options; 1)get a lot of ventilation and get a lot of noise or 2) conduct the heat to the outside. Check this website, step 16
http://www.ifixit.com/Teardown/iMac-Intel-27-Inch/1236/2 you see apple used fans but also huge pieces of metal to conduct the heat from the GPU and CPU to another place. Well your macbook (if it's a unibody) uses the body for this. So when your macbook pro get's hot, that's because it's conducting the heat. So how hotter, how better (as the heat get's conducted away from the cpu), although too hot isn't okay.
So apple choose both options, used low noise fan's and conducted the heat with the body. That's why your macbook can get really hot. And if you're a boy,
don't let your macbook sit on your lap 
.
But when it get's too hot, that's not okay as it damages the hardware. This happens when there's not enough could air to get in the mac (some people place there macbook on a pillow, blankets, or whatever which blocks the ventilation gates, not enough air get's into the mac, the mac get's too hot). That's why there are tables. Just use those. And probably hot places (like Nevada) will make that the mac can't conduct it's heat, so don't place it in the sun. Use it in the shadow (which your probably already do because of the glossy screen).
So when you use your macbook on your table inside where it's cool it should be okay. (even when it get's pretty hot).
