I signed up for VATSIM and ventured in once. I was more nervous on RT than in the real thing.
When I have used it for practice approaches etc. I turn down all the realism settings. What's important to me in those situations is the procedure as such not the actually 'flying'.
I agree with Coffin corner. It has it's uses but not good for PPLs.
I do have to say that in terms of realism, no 'toy' sim even comes close.