Since I first posted this solution it never happened again.
I had this problem but I found it was the settings that changed when mountain lion was installed.
Mountain lion changed my three finger gestures to four finger gestures when swiping between full screen apps.
I found there were extra settings. Apparently when installing mountain lion my three finger gestures were changed to four finger gestures.
My issue seems to be a bit different.
Since upgrading to Mountain Lion, it first seemed as if everything was running smoother, and faster. Over time, that's kinda slowly reversed. I get rainbow wheels all of the time now, just about daily, when I would get them maybe once or twice a month at most before ML. Safari gets them all of the time lately, and just a couple of days ago it totally froze on one after trying to zoom in on something I was reading, and I had to quit it from the Activity Monitor. I reopened Safari to find that it opened back on the tab that it was on when it froze, which is not my homepage, and it opened on the rainbow wheel, and frozen again. I then used the AM to close it again, then restarted my Macbook Pro Early 2011 edition.
After restarting, and in a ready to work state, I opened Safari again to find that it once again opened on a rainbow wheel, but this time on my homepage, and zoomed in to the max, and shortly the wheel actually went away. I then tried to pinch to zoom out, but it had no effect. I closed Safari and opened again, and finally all seemed normal, except I couldn't zoom in or out of anything, and I'm still having that problem.
It's very annoying for me, as zooming in and out is very useful to me with my bad eyes, and trying to read some stuff gets really tough for me.
Any suggestions as to what might have happened, and how I might go about fixing it?
All gesture settings in the system prefs are as they should be, I'm clueless as to what else to check on.
Thanks in advance for any help.
I think you have a completely different problem. (The problem that was discussed here was a bug that was fixed in a system update several weeks ago)
It sounds like you have an incompatible Safari plug-in. That would explain the slow downs, the spinning beach-balls, etc. The fact that you see it when zooming is, I think, mostly coincidental.
Try the suggestions on this support page:
The only problem with that advice is that it doesn't tell you which "add ons" you need to keep.
This is what I left in my "Internet Plug-ins" folder, I'm reasonably sure that these are the ones that come with Mountain Lion :
JavaAppletPlugin.plugin (though I'm suprised that this one is still there)
After you delete any others, start up safari again and see if you notice an improvement. If you do, try re-installing Flash, if you want it (you'll have deleted it by following these instructions) - make sure you get the newest version from http://get.adobe.com/flashplayer/ - and then test Safari again. Do the same for any other plugins that you may need like Flip4Mac and Silverlight (you need Silverlight if you use Netflix streaming) - always getting the newest version from the web sites.