[snl621]

I have been running the coreduotemp app in osx, and have routinely seen the mb reach 153 F, however, I went out for a spell when I was in xp, closed the lid of the computer, and left it plugged into ac. When I returned home I heard the fans spinning at a level that I had only dreamed of osx. Thoughts?

[alex_kac]

There is another thread on this in that OS X uses your graphics card a ton, while XP does not. For example, many people report that using Vista on their ThinkPads or Dells cause it to heat up unimaginably.

[harrisjamieh]

My MB is quite a bit hotter in XP than OSX - fans regulary come in under XP

[ghporter]

It will all depend on what you're doing with the computer. I don't see why one OS would stress the CPU more than the other, since BOTH have "idle processes" that watch for events and pass them on to whatever's running. There may be a minor advantage in one or the other, but I'll bet it's not enough to write home about.