I was going to post this in my top secret Good as Gold Ideas (tm) file, but I'll just stick it out here in the public domain for you guys to dwell on.

Acoustic Modeling Headphones (or Earbuds). When you walk into the room, they would use some kind of passive echolocation (or invisible lasers? uv/ir leds?) to create an acoustic model of the room and then the dsp in the audio player or headphone unit would model the room virtually in your sound.

Imagine...

While wearing headphones, you walk into a metal or concrete room and the reverb inside your head gets all springy.

Now wouldn't that be cool?

Of course, there's other things to worry about, like World Hunger...