Correct me if I'm wrong, but surely the whole point of a laptop design is to conduct heat out of the limited confines of the case to the wider atmosphere? If the machine case feels hot, it's surely because it's doing its job? Certainly, I'd rather have a hot lap than a hot chip. Anything that makes the outside of the case cooler is just building up heat inside the case. You may be able to make the chips run cooler, but that necessarily comes at a cost, either of increased fan action, and hence power and noise, or a warmer lap. I've got my MB on my lap as I type, and on a typical British late Sping night I appreciate the warmth (let's face it, people pay good money for heat pads for their laps!). If I was bothered, I'd follow Apple's clearly stated advise and put a flat surface between the book and my lap.
Seems to me that all Apple's done is decided on one particular, out of many possible, compromise between internal heat, external heat, and fan noise/power consumption. The solution they've come up with emphasises a warm lap and a quiet computer (my MB fan hasn't come on once that I've noticed in my first 10 hrs of use). I'm happy with that design choice: your mileage may vary.
