http://howto.cnet.com/8301-11310_39-...n-a-tv-screen/Cleaning a TV screen seems easy. Windex, right? Wrong. Most modern HDTVs have special coatings on their surface that can be ruined by strong cleansers.
I don't know if there are any special coatings on scanner glass but better safe than sorry. I don't clean the glass that much. A bottle of cleaner lasts years. You just need one small squirt.