I just noticed that today (or pehaps yesterday, depending on how you figure it) is the 6th birthday of the everything-list, which was begun by Wei Dai in January 1998. The list has remained remarkably active and civil over that time, compared to other lists I've been on.
The initial message stated, "You are invited to join a mailing list for discussion of the idea that all possible universes exist." This has spun off into a wide variety of related areas: logic, mathematics, physics, infinite sets, theory of computation, Godel's and Turing's theorems, algorithmic information theory, the philosophy of consciousness, decision theory, and much more. Although this list did not originate the idea, we have seen it grow from a little-known curiosity to a model that might be characterized as almost mainstream, including a widely read article by Max Tegmark in Scientific American on multiverse theory. For all the attention, though, it is hard to see much progress being made in terms of possible predictions that might allow, even in principle, testing the plausibility of the theory. I'd like to thank Wei and all the other contributors over the years for creating and maintaining a high quality and lively discussion group. Hal Finney