I've spent a surprising amount of time calculating the BPM (Beats per Minute, or tempo) of songs. I would always use a stopwatch, timing 32 beats to calculate the BPM.
Joerg Bitzer has made this a lot easier, and more reliable, with a recent submission to the File Exchange. BPM Counter
is a simple GUI that calculates the tempo of songs by timing my clicks on a button. This is some good stuff - I just learned that the Beastie Boy's classic "Fight for your Right (to Party)" is 134 BPM. This could come in handy someday ...
(In case you were wondering why I've spent so much time doing this, it's for one of my side jobs. In addition to being a MATLAB geek at The MathWorks, I teach aerobics classes. I used to make my own custom music mixes, and always had to sync up the tempos.)