1. Linux. Alright, the GPU seems to be a PITA but I was going to run it headless anyway, so does everything else work flawlessy and with open source drivers? Ethernet? SATA? Can you read temperature with lmsensors?
USB - yes
SATA - yes
Ethernet - yes (tried on ubuntu 8.4 beta only, but 7.10 dmesg says:
eth0: SiS 900 PCI Fast Ethernet at 0x2000, IRQ 20, 00:1c:c0:2b:8f:0f.
GPU - use 'vesa' drivers and you'll be fine for a headless machine.
lmsensors - yes! (ubuntu 7.10)
The module needs to be started, e.g. by adding them to /etc/modules
# Generated by sensors-detect on Thu Feb 21 22:47:38 2008
# Chip drivers
2. The running temps sound ridiculous to me. 80 degrees? But with 19W TDP this means that the CPU is not generating very much heat, it only has serious trouble getting rid of it, am I right? So the are coming through the whole case will be reasonably cool and will not destroy the PSU in the long run?
As you say, it does not produce that much heat. Problem is that the heatsinks alone are not sufficient without airflow. If you read the forums, most people find some sort of a sollution to make the system run cooler. Fan blowing across, underclocking, larger heatsinks, heatpipes, etc. I personally worry more about the (N/S) bridge than the CPU or the PSU.
3. Some you seem to have installed dual Thermalright or NC-U6 heatsinks. Who hot the North Bridge can actually get? Can't you just install the original CPU heatsink on the NB and high-tech heatpipe wonder on the CPU?
Hot? If my CPU sensor says 45deg, system 38 deg, I cannot keep my fingers on the bridge. (btw, I have a silent fan@~7V blowing across the MB from behind the CPU.). For heatsinks and such, please measure that first, there is not so much space available and there is only a tiny sort of clip to attach to the MB.