I've just starting using the online version of Rosetta Stone's language learning software. One of the features I like is the pronunciation practice, where you listen to a phrase pronounced by a native speaker, you try to say it into a microphone, and they then display several waveforms of each sample, and rate how well your version matches the model. It's not perfect, but it works pretty well.
Until the PowerBook fan comes on, which it does every eight or nine trials! Then, even a headset microphone picks up the little "whir, whir, whir" noise, and you basically have to sit and wait until the CPU cools back down so you can continue. Very annoying. Well, I came up with a simple method that so far has eliminated the fan noise with no risk to the electonics inside the PowerBook, and it's really simple: just unplug the power cable.
The CPU speed preferences are set to slow down when running on battery power, and running slower translates into lower temperature and no fan usage. In fact, after a few days of trying this, the fan came on only once, and that was when I inadvertently plugged the power cable back in!
There are probably other situations where this won't be acceptable, where the CPU needs to run full blast, and I'm sure that there are times with the fan runs even at the lower speed. But in voice-actuated situations that require less than full CPU speed, this hint may be helpful.
[robg adds: You could do the same thing with a custom Energy Saver profile under "plugged-in," of course. But if you did, you'd then have to undo it each time you finished what you were doing. Pulling the cable sure seems like the quickest solution.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20051104170421596