I just upgraded from CS5 and am encountering this as well. Zoomed out and I can pan very quickly around my document, but both zooming and panning around while zoomed in is excruciatingly slow and most of my pan scroll motions just move the document a tiny fraction of an inch. If you pause your pan motion before letting go of the mouse button it then pans the complete distance. The further I'm zoomed in the slower it gets, 300% is about perfect but closer than that it starts degrading. It also seems to be restricted to horizontal panning and not vertical.
This isn't a complex document at all with just a few lines of text and a couple shapes in black and white. It happens in both outline and preview view and I also tried outlining all my text to rule that out. My other documents also exhibit this but at slightly different degrees.
