6,603,350,897. That was the figure when I clicked on the US Census Bureau's population clock. At the same time, only 1,677,740 persons had visited Second Life within the past sixty days. And just imagine: 33,931 users online then, at a fairly busy time!
I don't know, it just struck me. Sometimes we get almost bored of talk about things like the 3-D Web, and take it for granted as we read about it daily in our multiple net feeds, etc., but it's not as commonly recognized as we sometimes think.