I'm positive this issue has been aired before, not just on this forum but many others. The issue - spinning beach ball with Mavericks. I have a mid-2011 base 21.5" iMac, the only mod being I took the memory up to 8 gig when first purchased. I don't drive it hard and having used computers from the early days I am in the habit of rarely having more than one programme open at a time. Even when surfing the net I don't tend to have more than a couple of tabs open at once. Up until I installed Mavericks I had never seen the spinning beach ball on my iMac even when running Windows in Parallels. Since I installed Mavericks I get the spinning beach ball often, along with bouncing dock icons and system hangs when the beach ball appears. I have spoken to Apple support and after they had me carry out numerous tests have given the Mac a clean bill of health. Rather curiously though they did say that if I could hang on until Yosemite then I should see an improvement. All this leads me to the conclusion that Apple have some issues with Mavericks which as per usual they are keeping tight lipped about. To be honest I wish I had never installed Mavericks and wish I could go back to ML. I've also notice the iMac running hotter since Mavericks too.