Several DJ apps appear to suffer at the hands of Apple with regards to accessing content within the iPod library. After many months of pressure, last year Apple finally gave the developers a way of reading files held in the iPod library. However, now it seems that access to the BPM ID3 tag (very important for DJ apps) seems to be either blocked or invalid meaning the BPM is always returned as null.
I only was aware of this after testing the latest version of Cue.Play.DJ which now has iPod library access and should display the bpm of the tunes imported. However, I suspect the impact of this will affect other DJ apps. This link was posted by Max (CEO of Capsulated on their forum today), I thought it would be of interest to other app developers as well...maybe pressure in numbers to Apple may get it fixed soon? (iOS 4.3 maybe?)