Just recently I came up with a great idea and I've also started the project.
I'm trying to create an in-car entertainment system. The raspi would be build in somewhere behind the dashboard en will be controlled via an android phone over bluetooth or wifi.
I've already started the programming work. I'm creating a mplayer frontend for playing the music, and will add some features to transfer music over bluetooth/wifi.
The only problem I have is that it takes about 20-30 seconds to boot on a clean debian install, this would have to drop below 10 seconds before it becomes an usable system (suggestions are welcome).
I hope I've enough time to finish the project so I finally have some music in my car without screwing up the looks of it.