I am firmly of the belief that the best team building excersize is doing the work itself.

In my experience "team building" is a useless exercise perpetrated by incompentent managers who fail to understand that the problems their company is experiencing are due to incompetent management. They see all the problems occurring in an area that they're in charge of - and they figure that the problem must be everyone else. So they send everyone else off to do something silly like building a bridge.