sandoz writes "Macenstein has up an interesting article with some evidence that running Safari seems to slow down unrelated programs. While the speed with which a browser renders a Web page is an important measure, the difference between browsers is usually a matter of a few seconds at most. To my mind, a more important measure of speed is how a browser affects the overall speed of your system."
Some responses to the article suggest that memory handling in WebKit may be the culprit. The Safari developers have already responded
to this article on the webkit.org blog. They explain why the slowdown might be occurring and how it's (probably) already been fixed in the nightly build. And they request more minimal test cases.