Solved: Safari frequently hangs with spinning beachball

TL/DR: Make sure your iCloud sync account is set up correctly, it can cause annoying Safari hangs.

I have been struggling with this one for a while and finally debugged it. So, I wanted to post the details here to aid any future searches for help.

Symptoms: Safari frequently hangs for 1-2 minutes after clicking on a link. It becomes unresponsive, but has the dreaded spinning beachball. Eventually that will stop, and the browser is usable again, but the hangs will recur often. Basically, Safari becomes unusable. I let the problem drag on for a long time, because I wad just using Chrome and Firefox instead.

I checked all the normal network, DNS, plugins/extensions, reboot, etc. But, nothing helped and all the settings were correct. Later, I noticed some iCloud errors in a system log and it occurred to me that it could be iCloud's browsing sync that could be the cause. Safari tries to sync the tab state of all browsers so they are available on your other devices. I like the feature, but it was the root of my problems.

I went into system settings and checked my account - triggering an iCloud authentication. It then triggered 4-5 other authentications, I guess one for each of the iCloud sync services. I also went into iPhoto and updated the iCloud settings there, because that was what the original iCloud logs I saw were for. But, I guess in the general case you should be able to get it updated by disabling then re-enabling iCloud in system settings.