Terra Nova has an interesting discussion going, talking about what really matters when we talk about a virtual world's population. Total registered accounts? Accounts logged in since last month? Concurrent users? Interesting stuff. From the article: "In a similar vein we discussed Second Life's 100K+ members, a figure which I and others have questioned here on TN. Cory Ondrejka said that SL's 'concurrency numbers are rapidly approaching 4500, about 17,000 residents were in SL in the last 24 hours, and 50,000 in the last 30 days... If you go back even 90 days you get about 90% of the accounts having logged in.'"