I have free access to Windows embedded version, so Im curious why go for it over a standard XP or windows 7 install? Isnt the embedded version a trimmed down version, sort of like TinyXP or Tiny7? Would that mean driver support is worse off? Driver support is crucial if you are using hibernation/standby because they can often break hibernation completely.
Any software that runs on XP will run on XPe, including drivers. XPe differs from TinyXP in that you build an image from the ground up from a choice of thousands of components, including custom components you can make yourself. In addition you have a number of deployment and servicing options that make managing numerous devices a lot easier. XPe is really meant for commercial devices, I don't think the development time is worth the effort for your single carPC. On the other hand, 2011 is much better and a cleaner, easier development experience so I would definitely recommend that even if it's still pre-BETA.