To be fair, I can see how assessment in SL would be a problem for some. As Richardson and Molka-Danielsen describe it, there are two types of classes in SL: "place of study" and "object of study" (49). If SL is being used as a place of study, then it is basically a substitute for a regular brick and mortar classroom and the fact that it is SL really has nothing to do with anything. As an object of study, SL is a main component of the class. The authors believe that when SL is used as an object of study, like in a composition classroom, then assessment is really nothing new. I would agree with that. I often use SL as an experience for students so that they have something to write about, or as a way for them to critique their own real lives. In this case, assessment is based on the essays they write: nothing new.
So it is when SL is used as a place of study that things become a bit more difficult. And this is primarily what Richardson and Molka-Danielsen discuss. They look at ways to assess language classes in SL. So, if you are considering moving your class into SL as a place of study, and particularly if it is a language class, I would highly recommend you read this article. But as for me..... not much in it that I was really interested in (or, to put it proper, "in which I was interested").