Everyone's heard of overclocking a CPU to wring the last few drops of performance out it, right? Well, a notebook jockey's equivalent is called "undervolting" and it's designed to increase battery life not clock speed.
An article in NordicHardware explains the concept:
The technology used is called undervolting and even if reducing the voltage would be a more precise description the name is still pretty easy to get. By lowering the voltage to the processor you can not only drastically lower the heat dissipation, but also increase the battery time significantly. There are, believe it or not, no downsides with this method, if you do it right. Therefore our new laptop writer Fredrik Andersson has written a guide that in detail shows how you to lower the voltage in a safe manner. The results achieved by Fredrik with his computer was 18% lower temperature and a 20% reduced power consumption.
Unfortunately the process requires three Windows-only applications, which means that you'll have to use either Parallels or Boot Camp if you want to try it with a MacBook or MBP:
Fredrik Andersson goes on to explain why CPUs are undervoltable:
Because CPUs are mass-produced, the voltage is set to a stable level that will suit all samples of that particular CPU. Everything from CPUs with “Friday Afternoon Syndrome” to real overclockers. There are lots of CPUs on the market that can be run at a lower voltage then what they are specified to. Especially the kind of low power consuming CPUs found in laptops. You'll be surprised when you see the results of undervolting your CPU.
You'll have to click through for the full results, but suffice it to say that Fredrik managed to lower the temperature of his Acer Aspire 5021WLMi at full load by 25°F (14°C) by undervolting. It's also important to note that his Acer has an AMD Turion ML28 1.6GHz processor. I'm not sure if you can undervolt an Intel Core Duo or Core 2 Duo.
I'm looking for volunteers to try this on their MB/MBPs. If you do, please post your results in the TalkBack below.