It's a few days old, but I noticed this article on /. about the Safari browser causing other Mac apps to run slower. I had just noticed the same thing yesterday. I was editing a slideshow in iMovie, tweaking around with durations and effects on slides along with the accompanying music. At the same time, I was also writing some code in XCode. I opened up Safari to check some C++ documentation, and it was like iMovie had been crippled. I didn't think it was Safari to blame in particular. I had opened a third application on a machine with two CPU cores, and both of my first two tended to be CPU intensive (encoding is never cheap, nor is compiling code.) Sounds like maybe I should have checked the documentation in Firefox instead. The reason I used Safari was because it is much faster at rendering most pages. I don't use it for everything mostly because it doesn't work as well with several Google apps I use a lot.