When I work in Photoshop I usually have my screen mode set full screen, so that I can use my screen to it's maximum potential and edit artwork that bleeds off the edges of the document area. I recently turned off my rulers (PC: CTRL+r MAC: Command+r) for even further maximum viewing area, and noticed that grabbing the page and moving it around was much smoother! I think the rendering of the measurement numbers and the scaling marks on the rulers in photoshop take some GPU or CPU rendering power away. Whenever I have the rulers on, it just seems to make the redraw of the entire window sluggish and choppy when I manipulate the document. I'm leaving rulers off from now on.