I was considering a Linux version of my software, but came to the conclusion that it would be too much work. I use a Flash frontend which would be mildly easy to move to linux, except that the only available SWF player doesn't support a lot of Flash's features.
The lack of decent GPS software in Linux is a major drawback. "GPS Drive" exists, but it's not very far along. Prehaps something should be developed which can read the map files from MapPoint or CoPilot. I was playing with MapPoint's ActiveX control earlier, and it's really slick. If I could figure out a way to read that in Linux, I'd be all over it.
The only person I know of that used Linux was ryanspc.com and he used to have a neat looking MP3 player which I'm sure I have stashed away somewhere. Now he just uses XMMS.