I have an iMac running Snow Leopard (Mac OS X). It's been running well, when I'm not using it that is. Of course I have managed to cause individual apps to crash and the sound card to stop working, and there was that one unfortunate incident when it couldn't find the operating system when it rebooted, but when left to its own devices, sitting there doing nothing but showing my pictures screensaver, the iMac has been fine. That is, until I started using Time Machine, the built-in backup application. As soon as I configured that to start backing up my computer, whenever it goes into the screen saver and stays there for awhile (an hour or more), I can't bring it back out of the screen saver. I get the spinning beachball of death, and it stays there until I run out of patience. The handy CMD-OPT-ESC trio doesn't "force quit" whatever is crashing, I have to hold down the power button to shut it down.
So for all you out there who are in the same situation as me, here's the fix: disable the Energy Saver. Found under System Preferences >> Energy Saver, set both the computer and display to never sleep, and disable "Put the hard disk(s) to sleep when possible." That's all it took for me, I haven't encountered the spinning beachball of death since.
Since I upgraded my MacBook Pro to Mac OS X Lion, I often encountered the Spinning Beachball of Death, especially when the computer screen wakes up from automatic sleep after some period of time. This happened even either the computer is connected to a power outlet or not. I’ve tried quitting resource hog applications (I don’t use Photoshop, iMovie, Dreamweaver, etc. that much) like Firefox, Google Chrome, and even iTunes, but the spinning beachball just randomly occur — the most frequent would be once a day.
Frozen apps happen to the best of us for reasons we don’t always understand, and a Mac application can just suddenly become unresponsive and we see the spinning beachball of death (sometimes called for short).