What should be used to clean the surface of the touch screen?
Totally agree. If the screen is just dusty, I keep my microfiber cloth dry so as to remove as much oil and dust as possible. However, if the screen is significantly dirty and hasn't been cleaned in a while, definitely go for a damp cloth. And to echo Steve once again, avoid ammonia/alcohol based cleaners. I find that a spray bottle full of water with just a few drops of soap does the job just fine.I just use a damp microfiber cloth. You can also use those cleaners made specifically for monitors and tv screens. Don't use Windex, alcohol or anything with harsh chemicals.
Steve