WOW Insider reminded me of the Warcraft Realms website and its wealth of stats on the European and US realms. If the stats are roughly accurate, there are over 3.7 million WOW players in those two areas.
http://www.warcraftrealms.com/realmstats.php?sort=server
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The Solo MMO Player collects links to the most useful or interesting MMO websites, databases and blog entries I have found, with a bias toward topics of interest to the Solo Player. Use the search box in the upper left hand corner to find topics. Kelari NPC Warrior art courtesy of Game Fluid.