Clay Shirky, for it is he, shaven headen and brilliant, has unpicked the current fad for SecondLife.
Clay suspects that:
I suspect Second Life is largely a "Try Me" virus, where reports of a strange and wonderful new thing draw the masses to log in and try it, but whose ability to retain anything but a fraction of those users is limited. The pattern of a Try Me virus is a rapid spread of first time users, most of whom drop out quickly, with most of the dropouts becoming immune to later use. Pointcast was a Try Me virus, as was LambdaMOO, the experiment that Second Life most closely resembles.
The data on the SL home page don't give much clue to its real popularity, although Linden's economist statistics do suggest some growth. But it's worh noting that the number of residents who are making real Linden $s has doubled from May 2006 to November 2006--what I don't know is whether that reflects the beta of SL's growth or whether this group of economically sustainable citizens is growing faster than the market.
Adam Reuters latest story seems to support Clay's thesis, pointing out that the number of in-game hours has only grown 29% between September and November compared to a doubling of the user base. This snippet of evidence would support the 'try me' thesis. Lots of one-off newbies fumbling about could easily account for the vast bulk of growth in user hours.
Clay is also skeptical about the source of the action in SL.
Many of the articles concern "The first person/group/organization in Second Life to do X", where X is something like have a meeting or open a store -- it's the kind of stuff you could read off a press release. Unlike Warcraft, where the story is user adoption, here most of the stories are about provider adoption, as with the Reuters office or the IBM meeting or the resident creative agencies.
Reuters, my employer, of course runs a bureau in SecondLife. This was an idea we pushed around over the spring and summer--and Linden Labs hosted me in May 2006. The rationale for a news agency being in SL has to be two fold. The first is that there is an audience there, a young audience, that is spending time there. News agencies want to get news to readers/viewers/viewsers, so following an emerging audience makes sense. The second is that SL might be emerging as a really interesting experimental medium, much as the Internet emerged in 1992/3 as an interesting place. So experimenting in that world makes sense--even if we aren't completely certain of the outcome.
Back to Clay, it is genuinely hard to sum up his rich essay in the time available so I would happily direct you to the source, if you are at all interested in the development of SL.