In the past, I've made the comparison of copyright laws and speeding laws. If you go faster than the posted limit you're breaking the law. Likewise you may be breaking the law by copying or sharing copyrighted materials. Doing either can get you a chat with the cops and some hefty fines.
Yet, the fact remains that most people speed. Some people are really egregious dangerous hotheads. But the vast majority of speeders are not those people - they're just folk who are making an estimate of the safe speed they can achieve, what the prevailing traffic is doing, and driving accordingly. Speed limits be damned.
Likewise, there are some really egregious copyright violators - factories in China that pump out millions of unauthorized DVDs. But most people are casual copyright violators, because they're engaged in activities that seem safe and sensible, such as loaning books to each other. What's necessary is a copyright enforcement regime that recognizes not all copyright violations are the same, and doesn't try to pile on ridiculous fines for sharing a few songs in the absurd hope that this will induce social behavioral change.
Cory Doctorow's latest column for the Guardian (UK) starts to sketch what such a common-sense + copyright scheme might look like. As a first step, he proposes that we re-establish the difference between commercial and non-commercial copying. The former, done in order to make money, would be treated differently from the latter. There are, of course, large gray areas between the two obvious extremes, which Doctorow acknowledges.
He goes on to give several examples of things that, applying a common sense test, would seem to be OK even though they might be thought of as commercial (e.g. mailing a copy of an interesting technical article to your boss). I definitely could quibble with some of his examples and I imagine many readers could as well. This is both on and off the point. It's off the point in that the specific examples don't necessarily matter if you buy into the principles behind them. It's on the point, though, in that what may seem like "common sense" to one of us may not be a shared idea of common sense to all. And "common sense" evolves, often faster than the law can change to catch up.
What's needed, I think, is a way to go beyond the simple phrase of "common sense" and to talk about what that might mean and how it would change. At base, though, I think we all agree that overly rigid copyright regimes serve nobody's interest.