I've heard of Droids not charging when it got too hot, but other than that, nothing function-wise. Perhaps you can rig up some sort of shade for the dock, so the Droid isn't exposed to direct sun?
i think the phone shuts itself of has happned to me were it gets REAL hot on NAV in the sun charging i had to hold it by the AC for the rest of the navigation so it wouldnt shut off again