I've used this for a long time, both in firearms and tactics training aswell as hand to hand. If you set up the training to mimic real situations then the airsoft can become a great tool for learning what is often difficult to teach using live firearms. Shoot/no shoot drills are my favorite as well as close quarters tactics that mimic what often happenes in a street confrontation.
As Jim said, don't treat it as a game or you wont get nearly as much out of it and it wont be realistic for all those involved.