Personally, I use Windex wipes (that I carry with me while riding) and Carl Zeiss lens cloths (designed for glasses and camera lenses). The lens cloths are more expensive, so I only use those now and again. As mentioned before, I have never noticed a problem with any kind of clouding or fogging. This being said, I probably replace my windscreens every few months due to, as mentioned before, scratches and what not, so I guess that I have never gotten to a point that I have used these products long enough to be a problem.
All this, I have heard that Windex can cause a yellowing of plexiglass, but I have never personally seen it. I won't use it on the windshield of my bike however, there I use soap and water only (just in case there is something to it).
I guess that there really isn't anything new in my post other than a confirmation that I have not had any problem using the Windex wipes in the past...they do get the bugs off pretty good. I do like the idea of rain-x on the outside and the rain-x anti-fog on the inside. Going to try and get some of both tomorrow and give it a shot...