On the new unibodies the keys do not touch the screen. Think about it, there is the rubber around the bezel of the screen that raises it off the surface of the aluminum (done to prevent scratching). Then there is the fact that they keys are recessed below the surface of the aluminum anyway, if your keys touch the screen on your unibody I would take it to Apple.
If you are talking about a preunibody MBP then yes the keys do touch the screen and I would suggest getting either a screen protector or a keyboard cover.