I used to have one of those massive 17" MacBooks (Best keyboard ever), and it used to heat up enough to turn my thighs red. Back then, Apple avoided calling them "laptops," perhaps for this reason.

Then I moved to Chicago, and found it was a wonderful machine for using outside on my balcony in cold weather because it would keep at least half of me toasty. If I started to get chilly, I'd fire up Virtual PC and snuggle in.