My Dell Mini-9 just came back from Dell service, and it's now a totally different experience. They replaced the motherboard, and possibly the CPU (I can't tell). With these changes, the box is performing just as expected, even when it gets warm. If you own a Dell Mini-9, I'd suggest you download Geekbench and run it at least 4-5 times. With the Ubuntu OS, it should score over 1,000 consistently, and with MacOSX it should score around 900.
The issue seems to be that with the bad mobo (or CPU), the CPU will throttle way too soon, and too much. The CPU is no where near the temperature levels where it'll throttle to save itself, yet it does throttle, severely. Before my repairs, I could get as low scores as 200 (i.e. less than 25% of expected performance). To me, this became painfully obvious when running anything CPU intensive, like watching a very high resolution movie, or compiling something.
Dell were way cool about bringing my unit back for service, and it took about a week from when I sent it until it arrived back home again. I'm very impressed with that.