I am always surprised when someone tells me they have never heard the phrase "virtual worlds (VW)" or "Second Life (SL)." At the rate these worlds are being developed, I expect that most people will have heard within the next year. And of course if the projections are correct, there will be close to a billion virtual world users by 2018.
Gary Hayes presents a nice (very short intro) overview in this video. The quotes used are great, and notice how many of these VWs are targeted to preschool and elementary school age children, currently the fastest growing segment.
2008 METAVERSE TOUR-The 'Social Virtual' World's A Stage - A Film by Gary Hayes © Personalizemedia 2008
From the publisher's "More Info" link:
"Over 50 virtual worlds featured including:
Second Life, HiPiHi, Kaneva, Twinity, ActiveWorlds, LagunaBeach vMTV. There.com, Habbo, Google Lively, FootballSuperstars, Weblin, AmazingWorlds, CyWorld, Whyville, Gaia Online, RocketOn, Club Penguin, YoVille, Webkinz, BarbieGirls, Prototerra, IMVU, Spore, vSide, Tale in the Desert, SpineWorld, Stardoll, The Manor, There.com, ExitReality, Vastpark, Qwaq, PS3Home, GoSupermodel, Grockit, Croquet, Metaplace, Coke Studios, Dreamville, Dubit, Mokitown, Moove, Muse, The Palace, Playdo, Sora City, Voodoo Chat, TowerChat, Traveler, Virtual Ibiza"