“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.”
–NYU prof Clay Shirky, writing on Valleywag about Second Life’s user metrics and how counting trial users for any service just isn’t the same thing as a committed installed base.