If you're talking about major commercial releases, such as the kinds of movies that you would normally go to a theater to see, the after-market has changed a lot. You don't have to go to a video store anymore; in fact, you don't even have to wait for the mail to be delivered anymore, because you can just download it if you have the speed for it.
Exhibition is becoming thoroughly "democratic." Anybody can shoot, edit, and publish a movie on the internet now. Whether or not it will be seen by anybody other than their immediate family is another matter.
I don't think the internet is going to kill the theater business anymore than television did, however.