SF author and EFF evangelist Cory Doctorow gave this talk at Microsoft discussing why DRM is a bad idea. His main points:

1. That DRM systems don’t work
2. That DRM systems are bad for society
3. That DRM systems are bad for business
4. That DRM systems are bad for artists
5. That DRM is a bad business-move for MSFT

Read the piece. Really. Pay particular attention to the first point: there’s a very simple reason why DRM cannot work as advertised, and he makes this point very, very clear.