digital-lifestyles.info has a piece on Twinity and Berlin, with some nice comments. They also cite some interesting potential issues:
a desire to live where lots of rich people are (London Chelsea, Mayfair, etc)
as the game become more populated, will there eventually be the same lack of housing that burdens the physical world, duplicated in the Virtual world?
This will indeed be interesting to watch, for both us and the Twinizens!