that's why i run mine in reduced mode 99% of the time.. whether plugged in or not. I just don't do stuff that requires lots of processing power... i guess thats a benefit. Hence the reason i bought a 1.33ghz G4 instead of the 1.5ghz G4 when i made my purchase. It stays luke warm when i have it on reduced. it's not so hot i can't handle it and it's not cool to the touch as if it were off. If I am doing some more processor instensive stuff i set it accordingly and plug it in.
But ya, when it's runnign like that it gets pretty warm. .but then so does my Dell with a 650mhz P3