Some innovative projects have started introducing games to their digital resources in order to enhance their metadata
The Galaxy Zoo astronomy site has just launch a new game which allows users to help suggest how galaxy collision and mergers took place.
Google Image Labeller has been around for a few years; you are randomly paired with another user, and you then work as a team to try and come up with words to decribe images that Google has harvested.
Precise and trusted metadata is time consuming and often a little boring to create. Any process, as typified by these games here, that can reduce the cost and the boredom should be explored a little more.