I find that even just after hours of using my PlayBook, the screen is littered with fingerprints. Not only that, it's also greasy. When I just use the cleaning cloth, all it does is smear it across the screen and doesn't do to well to the cloth either, as this will just transfer to other things I use the cleaning cloth for.
Haven't you ever heard of Carnauba Wax - just buff that smeary mess in one direction! I figure if it is ever stolen, there will be traces of my dna on it forever!