I've farted around with the thing and I'm not sold on the advantages of it, personally. My biggest problem with it is we only have one of them. It works well if you partner people up but with the eight week format of our classes, we don't have the time to cycle everyone through the virtual welder before getting them out on the real thing. It's fun to play with, however.
You can set up different scenarios where you'll be welding, different welding processes, different electrodes, material thickness, joint types and positions. The machine will tell you if the parameters are within the required range and then grade your performance on things like arc length, travel angle, speed of travel - all the things you would be looking at if your were actually welding. The view through the helmet is pretty realistic and you have to chip your slag like a real weld. And it has sound effects!
It has the potential to save a lot of money in material and consumables but the machine is expensive. You'd have to use it a lot to get the payback, however. While it simulates the welding processes very well, I'd like to see it make smoke and spit out sparks as well. Then you'd have something.