I'm surprised nobody has mentioned this for use as an input device. I'm still in the planning stages of my CarPC project, but this will be one of the input devices I will be using along with a Lilliput 7" or 8" touchscreen.
ATI has provided an SDK for the Remote Wonder I and II which programmers can use to develop plug-ins for various programs. Can't control your favorite media player using this remote? Search for a possible plug-in or write your own instead. Along with the SDK, they have provided a sample Winamp plug-in so that you can see how to write one for your own application.
http://remotew.free.fr/