I'm with Rico, I use deluted Windex and a soft cotton cloth to clean all my electronic equiptment and have never ruined anything yet. I've only had my NC for 3 days now and have cleaned the screen a dozen times already, I hate finger prints.
As many have said, a microfiber cloth works best with either distilled water or you can also use some LCD screen cleaning solution. I'd avoid anything harsh that contains alcohol or ammonia, but blowing some bad breath on it would probably be OK .