I've written an article on my blog on how to release your game under an open licence. I always think it's a shame when games, particularly free ones, aren't open licensed. You're already generously sharing your work, why not let others build on and adapt it?
However, some people have trouble figuring out open licensing, and many have fears about losing control over their works. I hope the article explains and dispels those fears, and I'd like your feedback.