Thanks for sharing your experience. I also have a couple of thoughts.
I started using the iskin cover on a white MB. I, too, thought the cover made it worse in leaving marks on the screen, until one day I noticed someone else's macbook with keyboard marks all over the screen but without any keyboard cover. So I know I'm gonna have to wipe the keys/screen regularly one way or the other.
As for the IS film, I hesitated putting it on my aluminum MB for a couple of days because of the 'nerd-factor'. I wish I'm one of those who couldn't care less scratching their laptops (the real cool one in Starbucks with too much $ to care). But I'm not that cool (let's face it, I'm hanging around a laptop forum on a Sunday afternoon). Since I move my MB around a lot at home (kitchen counter, table, den, couch, bed), a sleeve just won't do.
A Redtech screensavr will prevent those marks, I just received mine yesterday and it's great