Here our subject is listening to music as a method to relax. What might be useful is a device that sits on the listeners finger/wrist, and generates music with BPM that is in sync with the heartbeat and where you want it to end up, with higher BPM if you wanted it to speed up, lower to slow down.

Nice idea!

Here, music is being enjoyed in a group setting, generated by one person. A device that would improve this situation would be a recorder, with a bit of built in GPS in order to determine location, in order to create MP3 files of interesting musical occurrences on the fly and have them NOT be a mess of similarly named files.

Here, our subject is listening to music while studying. A device useful for making this study session more useful would be a timer style system, with low-BPM songs divided by high-BPM songs to create small pockets of studying, which is better for learning and retention of information.

In here, people are listening to music in the context of a video game, using the controller to interact with the music. A device to improve this would be a playback system to show the player what they did wrong and allow them to practice it, all while letting them see what they did in great detail (with video, audio, and tactile logging)

Hm...Doesn't the game already do something like that? If not, it definitely should!

In this final situation, a device is being used to play music through speakers in order for multiple people to use it, as an alarm clock or listening a device. A better version of this would contain song information on the display, increase power to the USB to enable charging for all devices, and a small wireless chip to sync the clock with the atomic clock.

The clock sync is a great idea...Does an external player have access to the settings on the iPod/iPhone?