Recently, I collected some data from Sourceforge, hoping to find evidence for the importance of copyleft. But I found something surprising: although there’s plenty of evidence that many developers believe in the power of copyleft, the one measure I could derive of how much copyleft actually works showed that copyleft made no difference whatsoever! If true, this means a lot of free software’s social theory is wrong and many things will have to be re-thought.