I've been looking at the price structure of HD movies from iTunes. As far as I can tell, it's only worth buying a movie if you're going to watch it 5 times or more. I have only had an AppleTV for a few months, so I though I'd ask about rental availability. Once Apple has a movie available to rent, is it available to rent indefinitely? Do movies eventually become purchase only? Although HD movie sales are new, I'm guessing that there is some historical information from SD sales and rentals.