I was tempted to get one for my 350D (Pack of 3 you cut to size from ebay, about £2 from a european seller I think).
Then decided against it.
Apparently it's not the screen anyway, it's just a cover, and they're available cheaply and easy to replace (just glued on). Not sure how true that is though.
I must admit I've always envied Nikon users, because I like their opaque screen covers, but the only ones I can find for my 30D are the flip up ones, which I dont like.