Let me tell you a story ...
The Nobilis Lexicon of the Lost 500 Years is pretty much wrapped up. I had a fabulous time making various contributions as the amazing Augustine "A.C." Casey, Chronicler of Marvels and authorized teller of the tales of tough-as-nails Jim Dunsmuir. Victorian aetherships, fairy armies, and vortex blasters -- who could ask for anything more?
The whole Lexicon concept is a great idea for setting up game worlds (particularly ones that the folks know something about). I keep trying to think of other applications for it ... (At the very least, I seriously need to keep dabbling with Wiki.)