Hello,
This is quite an interesting topic. I think it is quite easy to obtain a wealth on information on various aircraft, regarding performance data, V-Speeds, Checklists. There are many really good simulaiton products of various aircraft available, and there are many more in the pipe-line. The only real use I could see for PC-Based Flight Simulator, is systems-learning. Like others have point out, there is alot of information, and alot of excellent simulations of various cockpit in superb detail. You could "easily" teach-yourself the operation of the cockpit, not in ever aspect, but the useful bits.
On another note, PC-Based Simulators can't "simulate2 the true feeling of flying. I would think it would be very hard tocontrol a "real" heavy-jet after a few hours on a PC-Based Simulation. Even Full-motion, expensive simulators can't exactly replicate real flight.
So in conclusion, it's good for system-learning. bad for actual flight dynamics! Is it becoming too realistic? The question is, will it ever truely be realistic, the answer is no, so it can't be too realistic!