David Weinberger links to the Times, which documents how hard NBC tried to shut of American access to the Olympic opening ceremonies as they took place (NBC has exclusive US broadcast rights, and showed the ceremonies 12 hours later, in prime time):

In response, NBC sent frantic requests to Web sites, asking them to take down the illicit clips and restrict authorized video to host countries. As the four-hour ceremony progressed, a game of digital whack-a-mole took place. Network executives tried to regulate leaks on the Web and shut down unauthorized video, while viewers deftly traded new links on blogs and on the Twitter site, redirecting one another to coverage from, say, Germany, or a site with a grainy Spanish-language video stream.

Think of "the little dutch boy" and the dike - only with a lot more flow on the other side of the dike. This is going to be a less and less tenable idea as time goes by; the only thing outlets like NBC are going to be able to do is show live coverage, and then repeat for the more general prime time audience.