Have you been experiencing sudden slowdowns, color wheels, and general unresponsiveness that started within the last few weeks? The problem may be one of the latest updates to Safari, or rather, the interaction of an older Flash plug-in with the latest version of Safari.
Flash is a type of animation that is common to many web sites. In order to see it, your machine needs the Adobe plug-in for your web browser. The good news is that either your Mac came with it installed or the web sites that use it will offer clear instructions on how to install it. The bad news is, once you’ve got some version installed, it’s up to you to keep it up to date.
My belief is that the new Safari coupled with an older Flash plug-in is resulting in a glitch that is swamping resources on your Mac causing general system slowdowns. Quitting Safari will help for a time, but eventually the problem will return.
The solution is to download the latest Flash plug-in from here, then quit Safari and install it. Be sure to do this every few months (at least) to keep up with the newest release because nothing on your system will tell you when your Flash plug-in is out of date.