There is a large amount of study currently on virtual markets in things like MMOs. What I haven't seen much in virtual economies is the ability to loan or speculate, which drastically reduces some of the possibilities for economics simulation. The one counterexample there was the Eve Online player who ran one of the largest banks in the game, then absconded with everyone's money. The lack of any sort of enforceable contract law made any sort of repercussions difficult. Though, I wonder if his ship got blown up after that...
Personally I found it interesting when a game I play went through a large deflationary period when the game developers cut down the currency in circulation by aggressively banning exploiters and bots. It gave me a feel for what the economic commentators are talking about now with the possibility of impending deflation in the US.