It works great. In future it will be Applescriptable, so can be used from other applications. But the program itself support scripts. When there is an incomming call, iTunes (or other players) stops, and when hangup, iTunes starts again. In the future is is also able to use the mic and speakers from the mac. That would make a great carkit. Check out their site and forum to see the possibilities
I never tried it, so i don't know anything about it.
They both don't have an interface which can be used with a touchscreen, but if they support AppleScript, somebody could make a nice Widget for it, with BIG buttons.