It's great for email, but it can never work for movies, TV shows or music, because in the case of "copy protection" the receiver is also the person that the system is meant to guard itself against.So as long as you can keep a secret from yourself, DRM will work....
Say I sell you an encrypted DVD: the encryption on the DVD is supposed to stop you (the DVD's owner) from copying it. In order to do that, it tries to stop you from decrypting the DVD.
Except it has to let you decrypt the DVD some of the time. If you can't decrypt the DVD, you can't watch it. If you can't watch it, you won't buy it. So your DVD player is entrusted with the keys necessary to decrypt the DVD, and the film's creator must trust that your DVD player is so well-designed that no one will ever be able to work out the key.
— Pushing the impossible, by Cory Doctorow, Guardian Unlimited, Tuesday September 4 2007