Devon Strawn: Collective Type, Wikis, and Eigenmedia pointed me to Collective Type, a project to explore what happens if you let random people affect a font design. Each character in the final font will be composed of a combination of 255 images provided by visitors to the site.
While not suitable for use as a font for normal use, the font is possible to read, and it's an interesting experiment exploring ways to harness collaborative design.