IMHO... The only time a BPM count would be useful is when you're dealing with dance/techno music. And since the BPM counter works well with that kind of music, I don't see a reason to worry about whether or not it works for jazz...

In my spare time, I spin jazz music for swing dancers. I count BPMs of everything I play and have it all written down on the side. This helps when you're DJing live and you decide "I want to slow things down from 180 to 140, now what have I got near 140, hmm..." This practice is quite common among swing DJs and is a regular topic of discussion on the SwingDJs mailing list.

Part of why I love the empeg is that I have it stuffed full of swing music, playing at random, and it will often help me "discover" gems hidden within my own collection. If it displayed an accurate BPM count, that would mean I wouldn't have to measure it for my notes but could just write down the number.

(And, if 1.1 finally allows for skipless playlist editing, then I could consider using the emepg for live DJing as well.)