The whole benefit of having MP3s is the smaller size of the sound file. Being able to have 100 songs on a CD definitely makes it a lot easier to find a song to listen to when the DJs won't shut up during the morning drive. But, as more people get into MP3s and collections grow larger, there will be a greater need for CD changers, or better yet, DVD changers. I am planning on ripping 5,000+ songs to MP3, and to use a CD changer, I would need at least a 50 disc unit to hold every CD I put MP3s on. As far as how to control, etc. regular CD controls are fine, but the advantage of the ID3 tags needs to be maintained. A simple readout, similar to what many people have already built for their computers (like a 40x4 LCD) would probably be best for most people,and should probably be part of the in-dash display.