Over at Ars, a great story on a Cambridge student who mathematically worked out the spot at which copyright promotes the most progress.
Unsurprisingly, today's system is WAY off, bought and paid for by those who have no interest in progress.
Pollock's work is based on the promise that the optimal level of copyright drops as the costs of producing creative work go down. As it has grown simpler to print books, record music, and edit films using new digital tools, the production and reproduction costs for creative work in have dropped substantially, but actual copyright law has only increased.
According to Pollock's calculations (and his paper [PDF] is full of calculations), this is exactly the opposite result that one would expect from a rational copyright system. Of course, there's no guarantee that copyright law has anything to do with rationality; as Pollock puts it, "the level of protection is not usually determined by a benevolent and rational policy-maker but rather by lobbying." The predictable result has been a steady increase in the period of copyright protection during the twentieth century.