Unfortunately, copyright has expanded well beyond it's initial scope and purpose.
Copyrights were initially issued for a period of 14 years - this provided sufficient time (given the technology of the day) for the publisher to recoup the costs of publication. This helped provide an incentive for people to produce (and publish) works. Once this was over, others were free to use and expand upon the (now public domain) work.
Current technology allows this process to happen much faster - copyright terms should be getting shorter, not longer. Extensions are particularly egregious - one can hardly argue that Walt Disney wouldn't have created Mickey Mouse had copyright not have lasted longer. Works that are already created need no incentive to ensure their creation.
How sad it is that one of the biggest users of public domain works (Aladdin, Atlantis, Cinderella, Davy Crockett, Hercules, Jungle Book, Peter Pan, Pinocchio, Robin Hood, Snow White, Sleeping Beauty, Three Musketeers, Treasure Island - to name a few) is largely responsible for it's demise.
One need only look at the lack of good media recently to see what effects copyrights have on modern creativity. So manys are remakes, adaptations, or sequels (Get Smart, Bionic Woman, Hulk, Speed Racer, Iron Man, Chronicles of Narnia, Lord of the Rings, Spider Man, Indiana Jones, Jurassic Park, Harold and Kumar, Batman, X-Files), etc.
How much better would it be if everyone was free to innovate, reshape, remake the work of others, instead of simply rehashing their old works over and over again? Wouldn't that serve to "promote the progress of science and the useful arts?"
If the current system doesn't serve such a purpose, would it not then be unconstitutional? Aren't we paying a very high price for something that offers so little in return?