I had recently installed the latest build of Webkit, WebKit-SVN-r34728, and while creating some email with my MBP 17" the fan suddenly increased speed. I have iStat installed. The fans normally at 2,000rpm were whirling at 5,400. CPU temps normally 54 degrees were in the mid 70's. When I popped activity monitor open is showed Webkit had climbed to the top of the leader board for CPU usage. I did some laundry and it was still there so I closed Webkit and things quickly returned to normal. Jim
Created attachment 21873 [details] Screen shot of Activity monitor while Webkit is using most of the CPU.
Is this reproducible? We're always interested in bug reports with specific sites that eat a lot of CPU, but vague ones that don't give us many details means that we can't investigate it to try to fix it. If you can reproduce this, in Activity Monitor, select WebKit from the process list and click the "Sample Process" item in the toolbar and upload that output to this bug report. I'm going to guess that you had a site, or several sites, that were rather Flash heavy, which eats an insane amount of CPU (you can tell whether it's Flash or not by the symbols - something to the effect of FlashEnforceLocalSecurity is the Flash plugin).