Apple finally confirmed what some Mac OS X 10.6 users have been reporting: There's a bug that can cause data loss when logging out of a Guest user account.
An Apple spokesperson stated "We are aware of the issue, which occurs only in extremely rare cases, and we are working on a fix," according to Fortune.
The bug in question is resulting in the loss of data in a user's Home directory when logging out of a Guest user account. Instead of deleting your personal data, the OS should delete the contents of the Guest user account.
The problem seems to be limited to Mac OS X 10.6 users that upgraded from Leopard to Snow Leopard and already had Guest Account support turned on in Leopard. The issue also seems to be limited to only some Snow Leopard upgraders since The Mac Observer wasn't able to duplicate the bug on our test system.
The bug underscores the importance of maintaining regular data backups and periodically testing those backups to make sure the data is intact.
Apple hasn't stated when it expects to release a fix for the problem, so for now Snow Leopard users should disable Guest Account support to avoid potentially falling victim to the bug. If you aren't sure how, check out TMO's article detailing the steps for disabling Guest Account support.