Derek,

Yes, push and pull refers to the amount of time the film is in the development stage, so if your pushing, you are leaving in development longer and if you are pulling your decreasing the amount of time in the development stage of processing.

Yes I have seen 200 pushed to 3200, not a pleasing result in my opinion, but it really depends on what your trying to accomplish by pushing it so far, it would result in a long time in the development stage to get a usuable image on a push of 4 stops like that, but indeed it is possible..

Dave