I am also able to get the app to crash quite regularly (segfault). If there are no files in the list (songlist) and you click on the list and then click any of the buttons the app crashes.
The system wont add mp3s into the database.
When the app loads with no songs.db i get a message: Can not enumerate files in directory '' (error 2: No such file or directory). The permissions on the directory are correct and this happens whether running as root or user.
another thing that I have also noticed while playing with the app:
mplayer under debian is not in the official branches due to some grey legal areas of it's code. more info:
headunit makes nice use of the xine-libs and could be an alternative player for your project.
Well it is a great start and i think that with some sourcecode you would get some help from some of the local linux developers around here ;).