This is plenty of time to exploit the financial possibilities of the initial release of a creative work, and it still allows remixes and adaptions in a reasonable time frame.
In a perfect world, copyright produced by big name corporations such as Microsoft would last 5 years or so, so that a product they make can mature, take market, they can make their profit, and then it goes public domain. They can still sell licenses for the automatic updates and such, and they don't need to make the source available - they just can't sue for duplication anymore.
Likewise, I would like to see independent content creators given a means to extend copyrights on things they keep iterating upon. An example would be Penny Arcade - it started as a small venture and has since matured to a recognizable standard amongst game circles. However, Tycho and Gabe continue to make comics and have been doing so for ~15 years. I figure their early work should be public domain by this point (consider how few people read the entire archive of their comic that far back) but they should be able to file a renewal after 5 years to double a copyright to 10 if they are actively iterating on a copyrighted product or concept.
I could settle for a blanket decade copyright if it included patents. Everything copyrighted expires after 10 years without exception under any circumstance and after expiration duplication and reproduction is no longer restricted to the copyright holder. Reproducing content and material becomes the responsibility of the one seeking it or someone else providing it, such as when the patents on some car engine expire after a decade of being on the roads, you can reverse engineer that engine without fear of patent infringement but you still need to take the steps to actually rebuild the thing.
That last point is important to understand. Just because something goes public domain doesn't mean that the original manufacturer (example, the car engine) can't continue to sell that engine. They can sell it for whatever they want. Having patents expire just means their competitors can copy design decisions in that engine after 10 years to improve their own engines and sell them competitively.
Same thing with media. Piracy only exists because the cost of reproduction is near 0 for almost any digital data. But people would still pay for features - Steam games could sell for a dollar or two to have cloud saved games, screenshots, built in recording features, etc.
And then when the steam platform passes into public domain, that doesn't mean Valve can't sell games with it - it just means people can alter or reverse engineer the software if they have it and if they want to and sell it however they want. But Valve would still have all the servers, and would be selling the usage of them - and they don't just become public goods. They are always private property.
The legal part is important , because there would be a good business model in simply taking all of the copyright expired works and creating a download/streaming website for it all and charging basically for the bandwidth and easy UI, not to mention that every TV manufacturer would want to integrate this.
That would be a massive library of stuff, far more than you could watch or listen to in your lifetime, would you really be worried about seeing the newest blockbuster the day it came out?
I think a lot of people want to keep up with the latest media, and there are lots of social reasons to do so. The latest TV shows, movies, and books will be the ones your friends are watching/reading. As xkcd eloquently put it: http://xkcd.com/606/
This points out one more factor: content prices decrease dramatically after several years. Videogames go from $60 to $10 on Steam; Movies end up in discount bins; books end up cheap on amazon or from used bookstores.
Books are an interesting example: when they are first published it is difficult to acquire them at a local library (because lots of other people want to read the same new book), but after some time (usually much less than a year), they are easily acquirable for free. If the library model works, such that authors are satisfied with the profitability of writing books, then reducing copyright term to a few years is probably reasonable.
EDIT: I personally think somewhere around 10 years is probably more reasonable, but I think the discussion around a more extreme 2-5 years is interesting, and the current term length is ridiculous.
I suspect the business model that is most likely to work is an extension of the current one.
Larger multiplexes with more screens, when you go to the cinema you have a wide choice of movies to see.
Movies would no longer drop out of the cinema within a week or two.
In this controlled environment it is easier for the cinemas to prevent copying.
Only after a long cinema run would the film be released on DVD, after which point the copyright expires and you can copy to your hearts content.
I can even see this business model perhaps working for music as well.