Read about Shazam - a tune identification application on Slate the other day and have been thinking about all kinds of uses for it. The way the technology works seems to lend itself to a variety of other uses.
One thought that crossed my mind was to use the cellphone as a stethoscope that would match sounds against a database of healthy and unhealthy sounds so the user gets a sense of what if anything is wrong with them even without having seen a doctor. Putting diagnostic tools in the hands of the consumer of health care services could be both helpful and empowering.
Wildlife enthusiasts could obviously benefit from Shazam as could someone with a car problem. Instead of taking their clunker to a car repair shop they could have Shazam listen to the wheeze, grunt, rattle or shake and give them skinny on what might be ailing their vehicle. Identifying an animal or bird by the sounds they make would likewise become a simple pattern match.
You are probably only limited by your imagination when finding ways to put technology like this to good use.