An important paper from the late 90s

As data mining becomes an accepted methodology for studying virtual worlds, it's critical to remember that much communication takes place in private tells and is not captured in logs. This is a robust finding going back to text-based worlds of the 90s. For excellent treatment of this topic see Diane Schiano's paper "Lessons from LambdaMOO: A Social, Text-based Virtual Environment."

Not only do private data generally elude data mining efforts outside of experimental contexts (which have severe validity problems), what goes on in private in virtual worlds is deeply engaging. It can't be overlooked.