Apple has acknowledged a Snow Leopard bug which could delete all your data, according to Engadget.
Neowin describes the bug: The problem, can easily be reproduced when a user logs into the 'guest' account, either on purpose or by accident, and when they log back out of the account and back into their normal one, they find that their account has been fully reset with all data wiped and lost - the account is like a brand new one. The home directory still exists under "/Users/username" but is completely empty.
Apple says, "We are aware of the issue, which occurs only in extremely rare cases, and we are working on a fix."
Until that fix is posted we would suggest not using your Guest account unless you absolutely have to...
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Neowin describes the bug: The problem, can easily be reproduced when a user logs into the 'guest' account, either on purpose or by accident, and when they log back out of the account and back into their normal one, they find that their account has been fully reset with all data wiped and lost - the account is like a brand new one. The home directory still exists under "/Users/username" but is completely empty.
Apple says, "We are aware of the issue, which occurs only in extremely rare cases, and we are working on a fix."
Until that fix is posted we would suggest not using your Guest account unless you absolutely have to...
Read More