Kind of Blue
One of the less well-known benefits of creating a commons is that it allows people to experiment with those resources in an unfettered way. This often means that they come up with new and exciting uses that would never have arisen had the underlying material remained enclosed.
A good example is Flickr. This is a tremendous resource, and people just keep on coming up with new ways of using it. The latest is the wonderful Flickr Color Selectr: just chose a colour, and the site will search through Flickr for cc pictures that match it. Not just useful, but highly therapeutic too, for when you're feeling kind of blue.... (Via Creative Commons.)