It's a pretty gray area! :)

I think the reality is that regardless of the license you pick, the user really does have the option of whether to include a link in the bottom or not. They could just violate the license and I doubt you're going to enforce it.

Here's my brainstorm opinion:

Leave the link as the default. Pick a license. Give them the option about whether to include attribution. When given the choice, I would think most would include it. I think things do spread by attribution. But they also spread by word of mouth/mouse. So twitter, blog entries, etc are what people really read.

MIT is a nice license because it gives the most freedom. I think it's particularly well suited for software or software components. It seems like lots of artists who give away their work like to use the Creative Commons Attribution license which allows people to use their work freely as long as they include credit and a link back to the source. FAMFAMFAM uses this for silk icons which you've credited in your footer on No Kahuna. This especially makes sense with icons, and other graphic forms of art that have no easy way to embed a credit or source.

I want the usage of Octopress to spread and my first thought was that a credit in the footer would be a nice way to achieve that, but I'm open to other suggestions. Wordpress uses a GNU license but they ask people to leave a credit in the footer because it helps the project spread, but say that they can remove it if they want to.

I want to do whatever will help the project spread but not irritate users. What do you think makes most sense?

I haven't done much looking at licenses. People seem to dig the MIT license. It's what Rails uses. Example in ActiveRecord:

== License
Active Record is released under the MIT license.

I'd like to specify that it must credit me, and link to octopress.org unless they want to arrange payment for an attribution free license. I'd be interested in hearing your thoughts on what license is appropriate.