I've spent many hours on FS2000 but only a few hours in a real bugsmasher with friends. All I can say is that I feel the FS experience puts me in a position of knowing what should be done - actually executing it properly would most likely be a different matter. Mind you, a few months ago I managed to land a quadrapuff motion sim reasonably satisfactorily even though it was a very long landing.
As an aside, a friend is a lightie instructor and has just passed his IR. He is doing his ATPL's and has actually been asking me to ask him questions about aircraft systems. Some of the recent FS2000 models (767 in particular) are extremely good replicas of the real thing (until it comes to handling)!