I have a real complex about the cleanliness of my LCD screens. They are pretty much spotless most of the time. As for the Mouse and Keyboard, I clean them when I see they're getting TOO far out of control. I find that if you wash your hands before you work on your PC it stays cleaner for longer (duh), but intense gaming makes your palms sweaty so it gunks up the mouse and some keys.

As for the general clutter around the PC room, well, let's just say I can still see the door.... lol