At least, in The Netherlands it is. The Dutch SL site secondlife.nl report a new milestone: 80.000 registered site users. That means 80.000 Dutch (and perhaps Belgian) people registered for this Dutch language community and site about SL. They reached this milestone in barely 6 months - 13.000 new users every month. That's quite a lot.
As a matter of fact, I can hardly believe these stats. Linden Labs puts the number of active Avatars from The Netherlands in may 2007 at 18180, or 3.37% of all active users. For earlier months only the percentages are available, and it usually hovers between 3 and 5 percent - under 20.000 active avatars per month. Add in Belgium, and it rises to some 26.000 users. Yet secondlife.nl reports 80.000 users..? Either they have an awful lot of users who've registered but are no longer active in SL or double registrations. But I can't imagine that a secondary community site like secondlife.nl could have more active users than the primary SL community.