Ok, well I downloaded a nifty new software program today that basically functions like the "Cool n' Quiet" feature of the A64, but it lets you configure the multiplier and voltage settings, along with timings for how long before upstepping, downstepping, etc.

For those unfamiliar with CnQ, basically it lets your CPU run at a very low speed (500mhz in my case) for nearly all operations, but will dynamically increase clockspeed as the percentage of CPU load goes up. So.. for example if my CPU spends more than 500ms above 90% load at 500mhz, it will jump to full speed (2075Mhz) and hold that until it spends at least 5 seconds averaging less than 10% load, at which point it will drop back to 1250Mhz, and if it still stays below 10% load for another 1 second, it will fall back to 500mhz again.

So long as your motherboard supports software control of the multiplier (and optionally voltage) you can use it on K6, K7, A64, and Pentium M boards. Here's a full review of it:

http://www.silentpcreview.com/article231-page1.html

All the newer AMD CPU's support CNQ. I have it enabled in all 3 of my notebooks. They never get a chance to use it since I have Folding@Home running on all 5 of my machines. I always strive to get the most efficiency from the machines I run. I really like the new Turion based notebooks! Mine draws 32W fully loaded as measured with Kill-A-Watt and is basically an A64 without dual-channel support.

My 4WD
Wife's 4WD

Seasonic S12 power supplies are 80% efficient compared to the average of 68% efficiency. This means less energy is wasted (released as heat) when the power supply converts the AC electricity from your wall to the DC that computers use. Because there's less heat released into the computer, this power supply is able to cool itself almost inaudibly with a slow, large fan. I highly recommend these units. They save you money over time, don't heat up the room as much, and basically operate silently. You can read about them and other cool/quiet computer hardware at SilentPCReview.

My monster-rig with a dual-core Athlon X2 uses 228 watts (1-2% margin of error) when both cores are used at 100%. A 65% efficient power supply would have required 350 watts from the wall and release 122 watts as heat for my A/C to remove. The Seasonic S12 only requires 285 watts from the wall and releases 2.1 times less heat, 57 watts.

Of course, like car engines, the best way to use less energy is to have a smaller and less powerful one to begin with. For example, my office computer uses an energy efficient Athlon 64 'Venice' processor and only uses 120w at 100% cpu usage, despite being overclocked nearly 50%. That's with a 3d video card that sucks up 20w of that total and while using Seasonic S12 power supply. With CnQ enabled, it idles around 80w and emitts next to no heat out the back. A similar speed Intel Pentium 4 system uses that much power at idle and considerably more under load.