I can add a few lines of code to estimate BPM if you were looking for something like that.
The main issue is that the estimated BMP changes during the song. Hmm - Perhaps the whole song can be analysed and then the bpm worked out after it has finished. That sounds like an interesting project to me 
I'm using an rMP3 board for my audio stuff (which will analyse the frequencies of the audio you are playing - so you can do visualisers) so I can also easily tell when the song has finished. Unfortunately my projects meter is already full so I don't think I want to try this right at the mo 
Btw, Rogue Robotics are currently doing a compo where you can win an rMP3 - see http://arduino.cc/forum/index.php/topic,50016.0.html
Mowcius