... vibration in a car? If someone (a passenger, obviously) were to be touching this thing up as the vehicle is moving, wouldn't the vibration from the screen be lost amongst the vibration already being experienced from the vehicle?

And call me old fashioned, but isn't the surest sign that your input was registed that whatever you asked to happen, happens? I'd much rather 'I asked it to do it and it's done' than 'I asked it to do it and it'll get to it in a while but at least my finger is lightly massaged while I wait'.

Make stuff go faster!