It seems a bit strange, but apparently it's happening for social psychology, examining how people interact in groups.
While the idea is good and it is easier to get large amounts of people to participate in a game than it is to get them to help research, there's got to be some major difference between RL and SL. For one thing, there's a known correlation between Internet personas and people acting like idiots (see the Penny Arcade cartoon - warning, expletives!)
Hopefully the scientists have the sense to take that in to account. And the fact that they'll mainly be monitoring geeks/gamers and not a good cross-section of all of society.