Erik Hatcher - Lucene Summit:

"I really found the Collex interface concept to be very interesting. Everything is a contraint or limit and you can easily add or invert the contraint. It’s also easy to add things to a personal collection and parts of the personal collection then become facets/contraints themselves. He’s really using all of the metadata (archive and user) to it’s full extent. He also has more plans including “exhibits” where people can “curate collections”. These collections themselves can then become objects in the index and so on. "