I got a demo unit from the MP3Store to check out. It is a REALLY slick little keyboard! The size, the clamshell cover, and back lighting make it just perfect for the CarPC! The its a perfect little "thumbs" keyboard. Very responsive, and actually can type pretty quick on it.
The Mp4Car store is planning to stock these keyboards soon as far as I know.
This image gives a good idea of just how nice and compact it really is:
