There was a time when Safari was the fastest and the best webbrowser on the mac. It was my default browser for more than 3 years. But one thing has changed it all:

Flash.

It started small, like only one annoying flash applet on webpages that I used to read. It wasn't doing much that could not be achieved with animated gif or png. Apart from eating like 100 times the CPU power.
It did not worry me that much, I could set most of them to "hidden" with my user stylesheet in Safari. I did not notice that people all around me started cutting down the number of open pages in their browsers to only one, so that their computer did not slow down to a crawl.
But now the times have changed. Webdesigner startet using not only more and more flash-applets per page, they also started hiding them in the code, making it hard to filter them by CSS. The last drop was the switch to javascript based flash inclusion to bypass the filtering on the side of the user.
Within the last three months using Safari on my Mac has turned into a nightmare of slowliness. I could not switch of Javascript because I need it, and I could not switch of Flash because I also need it. Safari does not let me filter flash. What could I do?

Switch to Firefox. Install the Flashblock-addon. And there is no step three.