I think there is at least one simulator that can be used online. It may just be for racing or to simulate flying with others; like a computer game.

It would be pretty cool if you could set it up to work with an instructor. After a live training session at the field, being able to practice specific things on the sim, with instructor feedback, could be pretty valuable. Doing this would require student and instructor to buy the software and would mean the two have to coordinate a schedule. Maybe even make it so the instructor could throw in surprises like wind gusts, deadsticks, etc.