Check my sig machine
The computer is solid as a rock....it doesn't crash or overheat or anything. They're very well designed. Mine has dual 10,000rpm drives, a A64 4000, and an X850XT in it, and it's totally sweet. Go for it dude. Remember if you buy a Sn25P to download the latest BIOS otherwise dual core Athlons won't work in it....Have fun.
NINJA Edit: The PSU in the Shuttle XPC's is better than a regular Power Supply, its called a PFC unit. Google it to find out more (IE, a 350W PFC PSU can provide cleaner power under greater load than a regular 350 watt unit)