I am still not entirely sure that a virtual world is my platform of choice but I can see that there are areas where they would excel. One being if the entire content were online and centered on a core set of concepts. For these concepts the guided tour to discover the foundational information required to engage in a group forum activity would be a way to use both of these teaching modalities.
I also like the co-creator collaborative aspects of these worlds. How fun it would be to be able to create and possibly visualize in real time.