Not a bad idea. But by the time you fork out for an Apple wireless keyboard, Magic Trackpad, and the MagicTray… I'm thinking you could almost have bought an iPad and used that instead. (I'm assuming you can use an iPad as an input device for a Mac media centre?)
Is this true? If that's true, it would give me a reason to buy an iPad. Nothing would be better than a trackpad with a display behind it.