I think the majority of hard drives have a built in temperature sensor from which they periodically callibrate themselves. My old 30GB IBM GXP75 has one which I'm able to access using the IBM diagnostic boot floppy.
I didn't know that MBM5 was able to read drive temps but thats a really interesting point. I have a couple of Raptors and a Maxtor Plus 9 that I'll check out.
<b>Vorsprung durch Dontwerk</b>.....<i>as they say at VIA</i>