In Safari Preferences->Bookmarks, there is a checkbox "synchronize bookmarks with other computers using .Mac". If you disable it, quit Safari, and restart it has checked itself back on. You can even switch to a different preferences pan, like tabs, and switch back to bookmarks and it is re-checked. It seems that it does not actually ever get unchecked except graphically for the time that the pane is open. The result of this is of course that Safari engages in a lot of web traffic when shutting down, and a brief burst when starting up. This behavior creates problems because for security reasons it constantly must be analyzed to determine if it is actually a trojan input manager or other such malware that is resulting in the web traffic.
Confirmed that unchecking "Synchronize bookmarks with other computers using .Mac" does not stay unchecked using a local debug build of WebKit r24013 with Safari 3.0 (522.12) on Mac OS X 10.4.10 (8R218).
<rdar://problem/5316373>
Closing as RESOLVED/INVALID since this bug is in Safari itself and is not a part of WebKit. It will be tracked internally via the Radar bug.