An Amiga MP3 player in your car. I'm sure that it's technically very impressive, and as a personal project it's cool... but considering the size and cost of 'proper' MP3 players these days, it seems a bit, well, OTT. Don't get me wrong, I'm not slating the guys talent... just that there are easier/better/cheaper solutions to that problem.
Personally I just use a humble audio cassette player in my car. My god, how archaic!
If you want mobile computing in your car that can play MP3s too, get a gorgeous Sony Clie or (please God, forgive me for what I am about to say) maybe a PocketPC device. If only Psion had made a device the size of a S5 with the specs of the netbook. The next best thing to a portable Amiga IMHO.