Inspired in part by the work of the Free Software Foundation, Lawrence Lessig co-founded Creative Commons and has delivered a whole new world of legal content distribution and sharing like none other before it.
The instant appeal is to artists of all stripes (musicians, photographers, writers, et al) to provide a method of distributing their works internationally while still maintaining some sense of control over use.
Many Creative Commons (CC) fans discovered the licensing tools via use of blog software like Movable Type, which includes the CC framework within their blog configuration tools.
The licensing process is flexible and covers a broad spectrum of use to work for a larger audience. The licenses are explained on the CC site.
The appeal to web designers and developers is two-fold: 1) A tool to distribute designs/content they seek to leverage the viral nature of the Internet for (perhaps for promotion, or perhaps to draw attention to for commercial licensing or sale of the work), and 2) a content search engine to look for content available for use on web sites under one of the CC licenses.
This last being the most unique and sure to grow as more and more web clients launch blogs as or in addition to a primary web site. This opens a new avenue for designers and developers to find images, music and written content for client solutions.