The number of videos from various DRM paysites one can find on KaZaa or BitTorrent or Rapidshare are, I think, a clear indication of the ineffectiveness of DRM.

And... DRM tends to scare away good customers who happen to be Luddites and can't figure out how to view the files.

One of the more interesting - and promising - things is Digimarc's new technology that allows you to add code to the video that an individual customer downloads, allowing you to track exactly who downloaded it if it shows up somewhere. I would think that just sharing the idea that the file might be tracked back to the person who shared it would be at least somewhat of a deterrent toward piracy... but as Jasun said, good content is what ultimately will keep customers spending their $.