I found this list funny...
Highlights:
13. It is acceptable to listen to non-doomy music if you play it at 1/4 of its normal tempo.
44. If there are more than 30 beats per minute, the music is too fast.
154. If half the audience hasn't left out of frustration before you've finished your first note, then you're playing too fast.
http://doomish.com/forums/topic.asp?TOPIC_ID=1195