Most Sundays around 2pm PST, Second Life reaches its highest peak user concurrency for the week.* Yesterday that peak reached just shy of 58K (see screencap), evidently a new record. Impressive numbers, when you consider that maximum concurrency was only 20,000 in December '06, and only 7000, in June '06.
Of course, it's somewhat less impressive, relative to insider expectations.
Last January, after all, I predicted maximum concurrency would reach 100,000 by the end of 2007, and that was a more conservative guess to what Cory Linden had prophesied that same month: he expected a full 150,000 to be in-world at the same time. Judging by Tateru Nino's eagle eye, as here and here, max concurrency grows by about a thousand, every one-three weeks. So assuming we stay at that clip, peak activity will cross 60K in the next few weeks, and reach some 65-70,000 by year's close. Considerably less than what I predicted, and significantly less than Cory's prognostication.
The reasons for this shortfall are fairly obvious: consistent server/viewer crashes (nearly 25% per session, a figure that hasn't improved throughout the year), a continued failure to substantially simplify the UI, or make the first time user experience more immediately appealing. But considering the arc of 12 months, we are still looking at very strong (if not spectacular) growth.
* No doubt because Sunday afternoon on the Pacific coast is the most optimal day and time for in-world activity among North Americans, Brazilians, and Europeans who comprise much of the world's population.