This has been going on for a while now, even before the Snow Leopard update. I'd be using an application, then out of nowhere, it beach balls. The only way to regain control of the application is to switch to another one (click the dock, window, desktop etc.) then switch back. So far I've noticed it in Photoshop, Pages '08 & '09, Quicktime 7 & X, and now its beginning to creep up on Finder. It comes in waves; on and off. This is the first second time since summer that it's been happening. Anyone else had this problem/know a fix?