I use XP at work, carPC and home. I also have 3 different flavor of Linux (Fedora, Ubuntu, PCLinuxOS) on my other home PC via swap drive. I like them all. I don't use PC a lot at home but if I do, I just use either of the Linux. So far PCLinuxOS is my pick because it support all 3 usb wifi card I have while the other 2 flavor didn't support out of the box.
Back in the day, I used to spend hrs on the net searching for how to enable the US Robotic modem (winmodem and real-modem) to work with Redhat. Now I don't have that much time to dig the web for info especially, most search result from search engine came up with nothing related to what you want to look other than p0rn and how to make your d1ck grow bigger.
Anyway, with Linux, support seem to be better and sometime you have to spend more time to read and search to know what the hell the answer giving you really mean if you are new to the game. Also, linux folks are more willing to help compare to windows folks.
Now to the point is I won't use linux for carPC simply because there is more work involve to get it to work compare to just use XP as of now. Thing will change in the future, who knows.