A Simulator is an excellent way of keeping in practice. I used FS One and it was a great tool. Every evening I flew atleast for an hour. It helped a lot to keep my memory fresh and my reflexes (and doing the correct stick movements with the reflexes) quick. I flew a different kind of plane for 10 minutes in that hour. For example I would start of with a Mustang...fly that for a while...then fly a Corsair...then I'll fly with the Edge...etc etc you get the idea. I found that flying the different planes on the sim kept my mind sharp - because for instance the Corsair on the sim bounces easier than the Edge. Things like that. The great thing about the sim is you can adjust the wind etc.

Like Minn said - it's not a substitute - but it is great for keeping yourself in good practise.