Dr. Richard Bartle's keynote for the last day of IMGDC was quite possibly one of those events that defines an industry, creating a ripple that affects everything that comes after. He offered a stellar analysis of a key feature, and problem, in virtual world design, suggested a solution that seems obvious (in retrospect, of course), and wrapped it all in an outstanding and compelling metaphor.
The issue he identified was the dichotomy between open "sandbox" worlds, and constrained "game" worlds, where the players are basically on a scripted path, with the minor exception of the existance of pvp.
Dr. Bartle showed how this divergence was historically created by the original divergence in MUDs, which had initially included elements of both kinds of experience (game and social) but had diverged in the 80's into game and social worlds - a split that has been carried forward since then, to the detriment of all. Game worlds become ultimately repetive and meaningless, and social worlds are impeneterable and unfocused.
The ideal solution is to recombine the two, with scripted events and activities early on to educate the player and offer social context, and more open play possibilities once the players have learned the system mechanics and other components of their new world. Everyone benefits, as the players have an easier entry into the world, and a richer cultural base from which to start, but also have the freedom to experiment and create that game worlds so often lack.
The metaphor that consistently ran through the talk was of three young heroines: Alice (last seen in Wonderland), Dorothy (recently in Oz), and Wendy, who told stories of Peter Pan and Neverland. Dr. Bartle pointed out that the three illustrated the key play experiences outlined above: Alice's reaction to Wonderland was "Curiouser and curiouser". She was enchanted by the newness and sought to have other adventures as she explored a wide new world: the play of an open ended world of new creations and experiences. Dorothy on the other hand, immediately wanted to go back home, and mostly travelled along one track, the yellow brick road (untill she wandered a bit to take down the uberboss). And Wendy was the creator, who crafted stories of Peter and Neverland for her younger brothers, creating content for others.
It really was an exceptional talk... I'll try to find out if the slides are online, and post a link when I do.