Someone asked if you could play the Roku movies more than once, or something like that:

"Videos play back instantly on your TV. No waiting for a download. Purchases and rentals are added to Your Video Library and stored online by Amazon.com so you can conveniently watch them on your Roku player."

I guess that means they are permanently available, but stored on the net, so you can't share them with your friends unless they come over for a beer or you bring your Roku to their house.