I actually find I can't have any music playing in the darkroom. I get too distracted and I can't dodge and burn properly. I really need to concentrate on the metronome when dodging/burning and having music on is too distracting. Perhaps it has to do with being a musician. Not sure. Anyhow, I will sometimes put on talk radio, but I can't work properly during the commercial jingles.
Funnily enough that's exactly why I tend to listen to house and techno. Not nearly as distracting and fast paced as trance, but with a defined pace that serves as a sort of internal metronome for me. I don't use it to measure precise amounts of time, but I often keep my agitation of my trays timed to the 4/4 beat in the track. 124-127BPM seems to be just perfect.