Rumors are flying that Apple will announce that the iTunes store will start carrying movies. Apple will hold its annual developers conference in a couple of weeks, and lots of people expect that Steve Jobs will show off the ability to download a movie and watch it at home. Supposedly Apple has struck deals with many of the major movie studios. What is likely is that the movies will have a time stamp that will allow you to watch them all you want for a limited amount of time (like a week or two). This would mirror going down to Blockbuster and renting a movie.
Of course, you will have to have a good broadband connection to do this, and services like this will begin to separate the men (cable modem broadband) from the boys (DSL). It is going to take a LOT longer to download these movies via most residential DSL connections (perhaps 2-3 times longer). But some may not notice too much, as you will have to plan the downloads in advance. Even with a cable modem, we are talking about hours, not minutes, and most people will probably order movies the night before they actually want to watch them.
Movie rental stores like Blockbuster are going to feel the squeeze unless they can develop their own download systems, which has been the Netflix plan all along (note that they did not call the company "Mailflix").