An extremely barebones music player for the car is hardly a terrible idea. PlayNow’s approach is to put one play button in the middle of the screen; you tap it to start the music playing, and tap it again to pause. You can activate shuffle mode by shaking the iPhone, skip to the next track by swiping right, and navigate to the previous track by swiping left.
However, the app incapable of playing any music on its own; instead, you have to use the iPhone’s native iPod application to start playing an album, playlist, artist collection, genre, or so on, then exit the iPod app and run PlayNow, after which you can use its simple controls to affect playback.
This may not seem like such a limitation, especially in the free version, but plenty of other car apps offer equally simple controls without forcing you to jump through those hoops.