The DMCA is both very good and useful and incredibly evil.

It's good in that ISPs can provide a structured method for content owners to contact them and request the "take down" of their material and be otherwise absolved of any requirements to research the copyright status of the materials they hose.

It's evil in that people who aren't content owners tend to think that they can send "take down" notices themselves. And it also tries to outlaw circumvention of DRM, even when you are just circumventing the DRM to do things you are otherwise allowed to do.