How to debug Safari CPU utilization and spinning beach ball? I have been plagued by performance problems in my late 2010 MacBook Air for several months now. Most of it seems centred around Safari. I regularly get very high fan speeds (loud to the point of very annoying), very warm laptop, high load average, and spinning BBOD (beach ball of death), especially on Safari.

I consistently have a single window, 8-10 tabs, none of them heavy dynamic apps (Gmail and Calendar running in Chrome). 

I regularly have CPU spikes from Safari and WebContent (and at times soagent). They rarely last very long, but when they do, I see the BBOD and Safari is completely unusable, then the rest of the laptop slows down to a crawl.

I have taken a spindump of Safari - it takes a very long time - but I do not actually know how to interpret it to see where it is stuck. 

I have almost no extensions installed. Just 1Password, AdBlock and ClickToPlugin (which was installed specifically to prevent Flash and others from bogging it down).

What can I do to narrow down the issue?
Adblock runs against every frame in the page. This is probably not all of your problem, but it is significant, at least it was for me. Switch to ublock and you should see a difference. Read the advanced docs and graduate to the the firewall style usage of this tool, and you will be very pleased.