Here's a technology in search of a killer app: Echo Nest is a web service. Send it an MP3, and it will send back a 800k XML file containing details about the track, from it's basic BPM to it's detailed structure, melodic content and dynamic range. You get timecodes for the start of each beat (or 'tatum'), then details of the loudness, pitch etc of each 'tatum'. Among other things, you could use the data to automatically chop a track into perfect loops.
It seems like a phenomenally powerful tool, but so far Echonest don't have many ideas what to actually do with it. Their first showcase is This is my Jam, a lame-ish widget to create automated beatmixes with predictable results (Tiesto to Tiesto = Good. Sabbath to Sinatra = Bad). For me, the first sign of real magic is The Jingler - a little novelty Christmas site coded in 12 hours last year. Using the API, it picks hitpoints and overdubs sleigh bells playing perfectly in time onto any song you upload. It's pointless but really clever. If you want to experiment with the system, you'll need to navigate their baffling site and apply for an API key. If you come up with anything cool, do let me know... (Image is 'Black in Black' through Adam Glazier's Echo Nest visualiser)