Photoshop CS5 seems to be getting more laggy. It's lagging heavily on large brush strokes and suchlike. This is on a regular A4 sheet with an average (12 ish) number of layers consistent with an average painting, and something I could do with barely any lag a few weeks ago.
Also, possibly relevent, my Tablet pen's forward button is lagging -very- badly, and very recently, the button that lets me drag around the canvas, now when pressed moves sluggishly and laggy. Used to do is sporadically and could be fixed by restarting pc, now it's permenant (and seemingly non Photoshop specific, does it in firefox too)
This could be a video card/driver or VRAM problem. Do you have the latest driver?