I'm writing a larger essay on this topic, but I recently posted the following to Interesting People and it was requested to put it here. It relates to the theme of "light" DRM.

I used to wonder if you made a DRM system that was so well designed that only a serious pirate would notice it was there, if this might be a workable system.

But now I have come to realize that there's one very important community which a DRM system can't avoid harming, and that's the open source
community, who as a largely philanthropic effort build linux, the bsds and much of the software that runs the internet and is thus used by everybody.

One of the pillars of the open source community, written into several of its most common licences, is that the end user must be able to modify the software, both for their own use and to give away to others. Of course, most end-users don't recompile their tools, but a sizeable number do, and they provide innovations, fixes and improvements that get used by all the users.

There is a fundamental incompatability between this ability to modify and any DRM that has a software element to its enforcement. You simply can't have them both.

That leaves DRM where all the enforcement (ie. decryption and display/presentation) takes place within physically secured devices. This is not easy to do, and even if done, it bars the open source software from any useful features that might be thought up which require access to the media -- only what the hardware permits can be done.

The end result is to largely shut open source software out of the media playing arena, and thus, if you believe in the convergence of media playing devices and computing devices, out of the general purpose home computer arena.

To those who use the open source software, the trouble with this is obvious. But in fact, all must be concerned, as the open source software, aside from being one of the few competitors to forces like Microsoft, is also becoming a source of significant innovation. That old style, garage-based innovation, where a loner or small team develop something new on the cheap which changes the world. DRM systems can be architected to allow a Tivo, but they bar the "next Tivo" which is a loss to all.

So the conclusion is that, as suggested, you can't pull off the "make everybody happy" DRM. Instead, you get DRM which mostly sits as a barrier not to pirates or users, but to the small innovators of the world, and what a tragedy that would be.