"Scratching" the platters is a non-issue. Most of the time they are made of polished Al and the magnetic element on them is pretty tough. What you have to worry about is everything from dust to finger prints. A single particle of dust in the path of the head is like a tree infront of a car.

This is offtopic but oh well.
A friend of mine has a fog machine he bought just for fun. I was staying the night with him once, and we got it out. We played with it all night, and set off the smoke detector about 5 times starting at 1 in the morning. His parents were pissed. Good time, good times.