This is something that I have experienced on two different iMacs (my old 2008 24-inch and my 2011 27-inch). It seems that at random intervals (no rhyme of reason), I would get the spinning wheel when I work in an application. It could be any application from Firefox to Football Manager 2010. I can switch to a different application, work there for about a minute, and again, the same spinning wheel (of death). Click on the menu bar, and same thing. So then I'm forced to hard reset the computer and turn it back on. It'll be fine for a couple of days, or as soon as a few hours, and then I'd experience the same cycle. I would also experience this if I leave home for several hours, come back, and the process begins all over again. I have to think that there's something constant built in OS 10.6.8 that is causing the issue. Any ideas?