Clickable Culture has a post describing the bad feeling left behind to the Second Life citizens by a real life company carrying out a failed experiment in Second Life.
I don't have any details about the experiment and hence not in any position to make any comment.
However, I know that there are many educators, tempted by the low cost availability of virtual world are looking at virtual worlds as a platform for teaching and learning.
I have been, and am now still not convinced that a virtual world with citisens of anything beyond your own class will be a good platform for simulations, role play or rule-based for educational purposes. I would question the wisdom of dropping a learner to the deep end of the pool in order to teach swimming. The very nature of simulation is to reduce the complexity into a certain level which will provide a reasonable challenge to the learners, yet provide a safe environment for making mistakes and not overwhelming with complexity beyond the current level of the learner.
A persistent world, by its very nature, will have different levels of sophisticated participants. This is not necessary not a good or bad thing. However, from a teacher's point of view, getting the group to focus on specific agenda will become more difficult once people beyond the class participate in the activity. In the virtual world, some of the dangerous acts would have less consequence, we may, hence consider virtual world meeting the requirement of providing a safe environment for making mistakes. Unlike simulation which start from fresh everytime, the persistence of the world will mean any mistake will presist as well. Again, whether such persistence of mistakes is good or bad for instructional purpose is very much depend on how it is being used.
I am not drawing any conclusion at the moment. This serves as a "progress report" of my effort to understand how virtual world may be used educationally.