Ok, for the past many months I have been having an issue with Safari losing all of it’s cookies randomly. The Cookies.plist file would go empty thus losing all my logins for websites. I was not able to figure out what was eating Safari’s cookies until just recently.
There never seemed to be a pattern to what was causing it. Not a specific site. Nothing l could seemingly track and reproduce. I always had a feeling it was caused by Mac OS X 10.5. The issue also appeared to be separate from a recent cookie issue that was fixed. But I might have found the real reason.
The desktop software Plaxo provides to sync the Mac OS X Addressbook appears to set tracking cookies in the Cookies.plist. It does this without even visiting the site. And it seems to have a habbit of destroying the Cookies.plist when it tries to update sometimes. This might be due to not using the Cookies.plist API, or it might conflict with an update from a website happening at the same time, thus nuking the file.
Either way, for the longest time my cookies would disappear multiple times a day. But now after removing the Plaxo software (partly a seemingly evil input manager) no more cookie destruction. If you have Cookies disappearing, and Plaxo for Mac installed. Do an uninstall of Plaxo and see if your problem goes away.