Daniel's blog has numerous tidbits on the platform's background, for the curious. At the moment the service is still kind of resource intensive, and you'll need Flash 9.0.115 and FF 2/3, IE 7/8 or Safari - Firefox 3 beta 4 might help. They made most of the games, and implemented an 'attention-based' currency that can be obtained from playing those games. Most of the avatars, furniture, and pets, though, have already come from the community. Plenty more details (esp. those for the technically inclined) are available at the Whirled Wiki.
A few thoughts on the project below.