Actually, you can rent movies and watch on your desktop (streamed through Youtube) or rent/buy books.
I would classify watching a full-length movie on a desktop/laptop computer as being pretty close to worthless.
My home television is driven solely by an ubuntu desktop. Works brilliantly. What's your qualm with such a setup? I've never been happier with a home entertainment solution.
None at all, I was talking about watching full-length movies on a desktop monitor / laptop screen. Sorry for the confusion.