I have just replaced my personal webserver, I was running an AMD64 3200+ in a standard tower case, it sounded like a hairdryer and if you placed your hand near the fan outlet it felt like one. I checked out what the recommended psu would be for this system just to get an idea of it's power consumption. I used this  PSU-Calculator  and it came up with a rating of 192 watts for 50% cpu utilisation.

I wanted something quieter and cooler that used less electrons, so checked out the Via ITX mobo's. ITX motherboards are tiny at only 12cm x 12cm and the VIA ones come with an embeded CPU and HSF. I opted for the VIA EPIA EN15000 and a Morex Cubid 3688 case with 1GB ram, a Laptop DVD RW Drive and a 2.5" Laptop drive. I use this as a webserver 24x7 for hosting this blog and I use it as a desktop at home. I have installed Visual Studio 2005 Pro and have had no performance problems. As a desktop it feels just as responsive as the old machine. It is not suitable for video rendering so I do this on my Duo Laptop but I only need to do this occasionally so no big deal. I know this system uses less than 60W because that is the rating on the external power supply. I estimate that at Idle it is using ~20W and it will be at Idle most of the time.

The other benefit is desk space the case is only W 20cm x D 27cm x H 7cm or roughly half the width of a standard Hifi separate with similar height and depth. The motherboard comes with onboard graphics, sound and GB Lan it also has four USB ports, S/Video and a RCA port which can be used for TV/Out or SPdif. The embedded processor is Via's 1500mhz C7 according to VIA this cpu at 100% utilisation uses only 12 Watts and has an average power consumption of 1 watt. How green is your desktop/webserver ?