In an article on C/NET.com, by Stephanie Olson, she explores this question.
My gut tells me that most kids probably won't suffer RSI injuries due to gaming or computer use. This doesn't mean that we shouldn't be more concerned about ergonomics in classroom/lab computer use or in game design. I know for a fact that my computer lab was not ergonomically designed and that the line of sight to the monitor and the posture of the kids while working was not ideal. (To say the least!)
I have come across articles concerning black-berry related injuries and since 1998 we have have been apparently concerned about "Nintendo Thumb". (I kid you not.)
Stephanie points to some real data that suggests that prolonged use of bad computer habits could ultimately result in RSI injuries. This is definitely something for ed tech enthusiasts to be aware of and concerned about.