To make a long story short, Safari has been good to me for the most part ever since I started using Macs. No major issues. Just now I tried to quit it. At the time it was using ~500 MB physical memory. As soon as I hit the quit button, it beachballed and my whole machine slowed down to a crawl as the "not responding" application used massive amounts of CPU (it was registering at more than 200%, and I only have two cores (!) ). Fortunately I was finally able to kill it from terminal. This is literally the first time Safari has done something like this to me. Any ideas on what might have caused it? The only major change recently was the 10.6.5 update.