In my mind this and the proliferation of, at best, highly questionable patents is the real problem. I don't see a huge problem with the duration of patents. In part because some really innovative technologies, medications for example, cost billions of dollars to develop and the time to recoup that investment is going to be longer than five years.
Similarly, though, even 20-year patents are devastating in industries that move at a faster pace (e.g., software). 20 years is an eternity in an industry where that same time span could see yourself through multiple major shifts in direction. Just imagine what would have happened if many of the early ITEF RFCs were patent-encumbered.
The duration of copyrights on the other hand are absolutely obscene. Even there five years is really short. I think the danger with such a short term would be that it would empower large corporations to some degree. After all other companies have the resources to go out there and compete head to head even if there is no copyright. The small content creator, without a major corporation behind him, is basically forced to try and compete in a wide open market. My guess is the small creator would just get crushed if anything he made caught the eye of a major company.
I have read where others say that the only copyright duration that makes any sense is the life of the author. I do not know that this always makes sense, but it does seem like a good upper-bound. I would, however, go further and say that copyrights should be non-transferable, and that the most an employment contract should be able to do is require an exclusive license for sale over a limited period. While the company is aiding in the creative process by pumping resources into the author, the idea still comes from the individual.
I think the real problem is that patents and copyrights have been corrupted. Both are good ideas and encourage people to invent and create things.
The problem is that we have no real way to validate this. How do we know both really foster creation? It can be easily proven that invention and creative endeavors existed before copyright and patents, so the burden is in proving that IP laws increase this behavior. But, how do you even test for this? With all the entrenched interests, you sure as hell are not going to get Congress to repeal IP law just to test the hypothesis.
You can even show cases where the opposite is true - where IP law blocks new inventions and/or creative works. But, how does this relate to the supposed incentives? Does it cancel out the benefits? Does it do worse? My gut feeling is that IP law is on the whole more destructive than helpful, but it is no easier (or possible) to prove this position than to prove that IP laws help.
The problem is they've both been corrupted to the benefit of a few entrenched interests. Copyrights in particular bear little resemblance to what they were supposed to be. I mean the whole point of them was to encourage people to create things so that the public domain would be enriched. Now they've become a tool for the virtual destruction of the public domain. Which is clearly not what was intended.
When you introduce big money into anything, expect corruption and perversion of whatever original intent there was.