This Lifehacker review says the apps that do this get it wrong 30% of the time.
(note to self: startup idea. BPM analysis software that actually identifies the songs instead; crowd-sourced corrections; ad revenues support the concept; the site lives for a year and makes a few million before others retrofit BPM into their own metadata. Maybe have for-pay API. Who wants to fund me? $30K 50%, six months product and biz development)