I just got Ubuntu Jaunty running on this cursed EEE 900, and noticed it was running hot. But I just turned on CPU frequency scaling, so now the machine can automatically slow itself down from 900mhz to as low as 112mhz.
Right click on the menu bar and click "Add to panel", then select "CPU Frequency Scaling Monitor". When I first did this, it complained "CPU Frequency scaling unsupported". Turns out the celeron needs a particular kernel module installed for that to work. Here's my source for this fix, translated from Italian.
sudo apt-get install cpufrequtils sysfsutils
sudo modprobe p4_clockmod
Then add p4_clockmod to your /etc/modules with your favorite text editor or by:
echo p4_clockmod >>/etc/modules