The World Stock Exchange (WSE) closed on 4th January 2008 for one month for "upgrades." As many coders who play the money market or read the news wondered, why the long shut down? Consider Linden Lab: they roll out upgrades across thousands of servers in a few hours of downtime, because they prepare and test the code in the background. Although we all cross our fingers the number of problematic upgrades is actually very small, and their code is millions of times more complicated.
Since then, WSE has decided to stop trading in Linden Dollars altogether, and reasserted the statement it is simply a game. This, despite having several people, including Anshe Chung, who are rather regarded as heavy-weight business people rather than merely players. There have been ongoing stories about businesses being delisted for bad-mouthing the WSE, even now it's closed - apparently blogging that you are considering leaving is enough to get you delisted.