I decided I'd make my content available with a CC BY-NC-SA (Attribution, Non-commercial, Share Alike) license, so that people could freely use and adapt my stuff, but would need to cite me as its source, make their content that was based on my work available for free, and slap a similar license on it. This is important, I think, to prevent the materials that educators make and contribute freely to the community STAY FREE. Without these stipulations (NC and SA), it would be possible for a commercial textbook company, for example, to grab the content I've created and add it to their "walled garden" of content which is technically free, but requires an expensive subscription to GET TO. This is a subversion of the Open idea which a lot of commercial publishers have tried, to reduce their cost of content and make themselves seem hip and up to date. The community calls it Openwashing.
A good description of openwashing. I've seen some examples of the practice in the wild, but should make a note to document some.