I've been using a MacBook for 6 years and just finally figured this out. Every month or so I'd have to clean off my screen. It had like a film over the entire screen and there were really no finger marks or anything. I read somewhere online that the screen kind of rests on the keys/palm pads and it transfers the grease to the screen. I even noticed this after cleaning it, closing it, then opening it later and marks being on the screen. So I've seen these cloths you lay over the keyboard to provent this. Are these worth it? Do they really work? Don't they get greasy and start making a mess too? I think I may have one that came with an iKlear pack I bought but it never fit right. I think it may be for an iBook.