When using a large radius on a box-shadow, on both Mac and PC, Safari 4 causes a massive CPU takeover in which just having it on screen can use up to 40% CPU and trying to do anything (hover over a link, type text in a text field, etc...) will spike the CPU to 100%.
It also makes the entire page pretty much unusable due to the lag.
I've done a test case here: http://tinycrumb.org/boxshadowcpu.html
Created attachment 33183 [details]
I can confirm this. http://identi.ca/ is very difficult to use, and scrolls very slowly. Offending item in CSS is "-webkit-box-shadow: rgba(194, 194, 194, 0.296875) 5px 7px 7px;".
probably a dupe of issue 22102
*** This bug has been marked as a duplicate of bug 22102 ***