I have an iMac Intel. I am increasingly bothered by the "spinning wheel of death" as I've heard it called, which blockes the computer for long periods, apparently without reason. Can anyone tell me :-what this is? How can I minimis or eliminate it?

Useful article here on the causes of the Spinning Beach Ball and how to troubleshoot it:

http://www.computerworld.com/s/article/9177479/Troubleshoot_the_spinning_beach_b all?taxonomyId=89&pageNumber=1

and also this:

http://www.thexlab.com/faqs/sbbod.html

What year, screen size, CPU speed and amount of RAM installed in your iMac?

How full is your Mac's hard drive?

How many applications do you run simultaneously in the background while working in another application?

Do you run any antivirus software on your Mac? Antivirus software can slow down the normal operation of OS X.

Do you run any "crapware" like Mackeeper or any other type of so called hard drive "cleaning" apps?

I have been to the Genius Bar 3x. It's not my hard drive, they said it may be the software and I should backup my data before upgrading to Mountain Lion but I doubt that's going to be the fix. They did ask "do you put it into sleep mode over night often"? I do, so they suggested I shut it down at night. Has anyone followed that advise and has it eliminated the situation?

Doing that will not solve your issues.

Look at my post above .

Can you answer any of the above questions?

If your hard drive is getting full, this can be one cause of beach balling.

If you do not have sufficient RAM, this can be another cause of beach balling.

Running antivirus software and other types of known "crapware" can cause the beach balling.

Running too many applications simultaneously can cause beach balling.

All of these issues together or in combination can cause beach balling.

There are other things that can cause OS X beach ball to appear. These are some of the more common ones.

Please tell us more about your iMac so we can better assist with your issues.

New Posters come here all the time, give us vague info about issues with their Macs and no other info about their Mac system and expect us to be able to help.

Please supply us with more information.

Michel,

So far after shutting the Mac down over night, I've not experienced the balling with all those other factors being held constant (running only excel, safari and iMail) with 16Gb RAM, the 500 Gb HD is not even 1/2 full. Though I noticed in ABOUT THIS MAC that I have 4 software install updates waiting.

Thanks,

Steve

Shutting down only returns a Mac to a certain default running state.

If the beach balling problem is there, it can and, most probably, will return.

Sometimes a shut down or restart can reset things, but if this was something that was nagging issue, it may return.

It's better for a Mac to sleep or hibernate than to constantly shut it down.

Shutting down and starting up a computer all the time puts more strain on electronic components than just letting the computer sleep and go into a reduced power mode.

Sometimes Safari ( or any web browser) can be the culprit as Adobe Flash Player, running inside Safari, can eat up a lot of CPU and RAM resources when on a website that needs extensive use of Adobe Flash Player. Also, animations and pop- up ads in a web browser can have the web browser using up more CPU and RAM cycles, too! Other web browser factors like having a lot of windows or tabs active can increase the amount of RAM that the web browser is using.

Also, it a good idea not to have too many CPU and RAM intensive apps running concurrently in the background.

Also, some unknown process can eat up system resources.

From time to time if the beach balling returns, launch Activity Monitor app inside your Applications>Utilities folder a see if there are any processes that are eating up an excessive amount of RAM or CPU cycles.

Any antivirus apps are known causes of OS X slowdowns and beach balling as well as a lot of " crapware" like MacKeeper. Keep software like that off of your system.