Well, my MacBook Pro recently refused to play any DVD's including the Leopard install DVD. I guessed that the DVD drive was duffed and was going to need a trip to the Apple store, since any DVD I put into the drive, it would spin and make a few noises before spitting the disc out again. My flatmate has a lens cleaner he bought for his PS2. I thought I might as well give it a bash, and rightly so the DVD drive works perfectly now! Saved me wasted trip to the Apple Store when a simple piece of dust was causing the problem.