This has been a topic of discussion around the web for a while now. Here are a couple of links discussing technologies for achieving this.
http://www.engadget.com/2010/09/23/adobe-shows-off-plenoptic-lenses-that-let-you-refocus-an-image-a/


http://www.nytimes.com/2011/06/22/technology/22camera.html?_r=1


I personally don't see it available to the general public for a few years down the road yet, and then when it does make it to the market, it's going to be a while before it is reasonably affordable to the masses.