I think a palm based remote is exactly the opposite of what is needed in the car, especially if you're going to try and emulate a remote type interface...

As you point out, there's no way to find a button without turning on the palm and then looking at the screen to find the button you're looking for. While I'm driving, I find it's hard enough for me to find my remote, feel around for the IR emitter to know i've got it pointing towards the empeg, then glace at it to try and find that button that i'm looking for... A palm just is too big to use comfortably and you're gonna have to use a stylus or get used to lots of fingerprints on your screen.

Touch screen remotes took off for a while in home theater, but when I read reviews of new ones a main feature is how many "hard buttons" it has because they're much more convenient...

All practicality aside, if you wanna do it, go for it. I won't use it, but there are thousands of others who might...

Matthew