I've been using my MBP for about 4 months now almost exclusively in clamshell mode (lid closed, external monitor connected). I started using it as a laptop now and I've noticed that the trackpad is a little warped. The middle is slightly dented inward. It can be seen with the naked eye, and can also be felt. I'm thinking of sending it to apple but I don't have any other computer at the moment so I may not. I am just warning anyone who is going to use their MBP in clamshell mode for a long period of time. I have the newest Penryn model.