Linden Lab's CTO just resigned, BTW, so citing him on this issue is kinda odd, IMHO. I would say no-one but Cory believed that 150,000 concurrency figure simply due to the horrendously overloaded Second Life instant messaging service, which grew something like 10-fold in less than a year and without instant messaging, the social aspect of Second LIfe, which most people agree is the most important part, doesn't exist. Some relief is on the horizon. Linden Lab is currently testing a new architecture to handle how avatars' computers interact with the entire Second LIfe grid and with the individual simulators, and this change should eventually bring about at least temporary relief from the instant messaging woes. Long-term relief will only happen when a radically new design for instant messaging is devised. Research by LL and confirmed informally by researchers at IBM, says that no current form of instant messaging will handle the "scary numbers" that will exist when virtual worlds come into their own, so the problem may improve for a while, then the numbers will exceed the ability of any current IM solution and we'll be left with another high-water mark for concurrency that won't be exceeded significantly until the next round of IM improvements is made. It won't be until a "real" solution to the IM problem is devised that concurrency in any virtual world or system of worlds will approach what all estimates suggest should be 10's of millions of online simultaneous users chatting away in a single inter-connected 3D system.

L.