My wife and I share her iMac, using two separate user accounts. My account is used almost exclusively for browsing the web. My wife's account hosts a large iTunes library, our iPhoto libraries (exponentially growing since our son was born). She also has an iPad and iPhone syncing to iTunes.
The problem that we're running into is that when she is logged in, she is running into these really onerous beachball episodes when browsing the web with Safari or Chrome, especially if she visits a webpage that has Flash content. She's also getting lots of beachballs in iPhoto when scrolling through the event list.
On my account, web browsing works fine. I don't have a significant iPhoto library.
I've looked at errors in the system console, and I've found and fixed a few problems that appear to be unrelated... some Chrome errors relating to extensions, which I have removed, and a bad print driver spewing log entries.
Where else should I be looking? I was a Solaris/Linux admin for 10 years, so I'm comfortable with the command line, but my Macs have pretty much "just worked" until now!