It looks like the new version of Mac OS X has shipped with a rather major flaw.
Users of the new Apple operating system Snow Leopard are experiencing massive data losses when logging into their machines under a guest account.
The problem appears to affect those who had a guest account enabled before upgrading to Snow Leopard.
Users have in some cases lost their entire main profile, including sites, pictures, videos and documents.
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Indications are that the Snow Leopard bug simply treats the principal account like a guest account - meaning that the account profile is wiped clean when logging out.
Users who first log into a guest account and then into their normal account have found it to be completely reset to factory default settings, with none of their personal data or files visible.
I'd advise not letting somebody log into that guest account just yet, and having a backup.