I'm working on a project that isn't exactly car-computer stuff, but may be of interest to people on this forum; it may even have a place in a car at some point. The project is called Dunbar and is a program for mobile devices (right now, Windows Mobile devices) that works like a social networking/chat program, but location-based. The program gets your location from a GPS receiver or uses cell phone tower data. It then shows your 'buddy list' by showing everyone's distance from you and shows their location on a map. The program requires a dataplan or some kind of connection to the internet, but the program takes care of the rest! It's free of course, and is in development, but there is a full working version, and web site to accompany the program. Check it out here:
http://www.warnockinc.com/Dunbar/
If you are interested in the program or helping w/ development, there is also a Google Groups page to discuss the project.