I have the iSkin keyboard protector for my iBook (it's the newer model as well) and I really like it. It doesn't affect the screen, doesn't affect my typing speed or comfort, so it's a big plus in my books. As for protecting, I've never had the experience of pouring anything on the keyboard, but it does keep the keyboard underneath free of dust and whatnot.
However, I have let others use the keyboard with the iSkin on and many (if not 3/4 of them) really do not like the feeling of typing with it.
Hope that helps.