BPM as a track level field wouldn't just be useful for DJs, you could set a filter which would keep the average BPM similar to prevent any jarring changes. I'm thinking a jump from a fairly sedate waltz to a polka would draw a lot of attention to itself. You could conceivably do this even limiting 'composer' to Johann Strauss if I recall correctly.

Mark
G68, baby Genelecs, Humax Foxsat, Oppo+Vanity93, Toshiba HD-A35, Pioneer CLD-925 + Meridian 519, various other random bits and bobs
Got a black G08.2 you want to sell?