Linden Labs releases May 2007 Key Metrics for Second Life and here's what I see:

    1. Total Hours spend in Second Life doubled between January 2007 and May 2007!  (Jan=10,817,668   May=20,767,557)
    2. Mainland Land use has doubled in the last 7 months (Oct 31,2006 = 83.97 while on 5/31/07 = 160.06).  Island Growth tripled to from 134.28 to 491.32 in the same period!
    3. Money being spent in world has grown 2.5 times since November 2006 - from 1,161,573,009 Linden to  2,831,517,265.
    4. Population has more than doubled since January 2007 to 6,860,473 registered Avatars to 4,370,810 individuals.
    5. Germany now leads France as the second most active country based on Avatar count.
    6. Woman are beginning to get more interested but Second Life is still dominated by men with 57% - but it's not as far part (Woman have 43%) so maybe it will get to be equal down the line.