Just unplugged my external keyboard, and lifted it up over my Pro and the USB swung and smacked the screen. As far as I can tell there's no damage, but am just wondering how difficult it would be to scratch the screen?
I've had my MBP for a couple years and no scratches yet! So, I'd also say they are pretty resilliant. If you're scared of getting scratches, there are screen protectors for MBPs that you could try.
I had a MBP 2,2 when they had the matte screens and it's still running great for some friends whom I gave it to last fall. It has no scratches on the screen at all. Though I was always careful with it so I never had any problems with scratches. I imagine the glass screens are more scratch resistant than the matte ones. Unless you drag some sharp metal or diamonds over it...