imac os 10.7.5 just lately, about the last month, i get beachballs. i have been told that this happens with low memory, and further that google chrome is a memory hog. i'll toss it if that's true, but i have also heard the same thing about safari. i mostly use firefox
If you have less than 4GB of RAM, that may indeed be the problem. If you have 4 or more GB of RAM, it is likely something else.
And if your hard drive is around 80% or more full, it may be that your drive is, for all intents and purposes, full, and your Mac can't run properly.
If neither of those are the problem, I'd run all of the suggested routine maintenance here:
OS X Routine Maintenance
OS X Maintenance And Troubleshooting
If that doesn't help, I'd uninstall any anti-virus software, and disable any login items located at:
System Preferences --> Accounts --> Login Items
If that doesn't help, try this:
Run Activity Monitor (in your Applications/Utilities folder), and
click on the "%CPU header", and then click on the triangle in the %CPU
header so that things are ordered in that column from largest to
least. Make sure that All Processes is chosen in the drop down menu at the top of the window.
See what is running that is using the most CPU time. If it
has a really high number, this is likely to be what is causing your
slowdown.
Leave Activity Monitor open while you work, and during one of the
times when your Mac has slowed to a crawl switch to Activity Monitor
and see if something is using up all of your processor's time.
Let me know what you find.
Likely candidates are a corrupted
Spotlight database, a corrupted Safari database, a bad stay-resident/
startup utility, etc. I can help you clear any of these problems
once we narrow it down. Whatever it is, it should be fairly easy to
fix.
More info:
Mac OS X Beachballs
Macintosh OS X Beachballs!