I've been perusing mp3car.com lately and decided it was high time I joined :)
I've been a Linux user forever and most of my development efforts are targetted specifically for linux. That said, I've found some of the efforts/projects people have been working on here very impressive!
Being a noob here I don't want to break any rules so I won't include the link to the site here, but I do have a linux-based system called "Silverwolf" that others here may find interesting.
The project is open source in that the source ships with every unit. The software is tied to very specific hardware so it's not all that useful as a generic frontend. It does use Xine and mpg123 for media playback, and uses the 2.6.11 kernel.