I've had some considerable success with online content selling, and I think that one really stupid thing the movie owners are doing with online rentals is limiting the time you have to watch the movie to thirty days. I don't see anything they gain from this, but I do see one important thing they lose: it makes the buyer be more reluctant to rent more movies at a time, because of fear of not getting around to them before they expire.
If instead they would set the limit to five years, or why not just forever, then, like I do with my Kindle book library, I would rent many more movies (especially at a three-dollar price), in the comfortable knowledge that they will sit there waiting for me until the day I have the time to watch them. I have at least a hundred books in my Kindle library I have not read yet, and I would not have bought them if there had been a time limit.
(I think with digital content the difference between owning and renting is largely academic, there are few books I read more than once. (And by the way, why don't they rent out ebooks, at half the selling price? They'd go like fresh cakes.))