Ed Felten, on Freedom to Tinker, writes a nice short piece explaining for the layman why DRM encryption is doomed to failure (Why Unbreakable Codes Don't Make Unbreakable DRM). I must note, however, that while the armored car analogy is very fine for explaining the issue, I do take exception to the fact that the consumer is analogized to a criminal trying to break into the armored car. In this analogy, the consumer is the bank official, who must have access to the interior of the armored car in order to do what bank officials (i.e., consumers) are supposed to and permitted to do.
We must remember that in order for copyright to be the engine of free expression that its proponents so loudly claim, fair use to comment upon, criticize and annotate the works must be available. The authors of the copyright clause did not anticipate an understanding of copyright that only permits citizens to be passive consumers of copyrighted works.
UPDATE 1550 ET 05 Dec 2002
Prof. Felten responds (More on Unbreakable DRM):
I guess I should have been more explicit about my assumptions. I agree that fair use is important and that treating your customers like thieves is a dubious approach. The point I was trying to make is that even if you're willing to ignore fair use and even if you're willing to treat your customers as enemies, you still can't build unbreakable DRM.