Apple has acknowledged a bug in snow leopard bug that could delete all your data. See details HERE
If you click on the guest account, you could loose the data in your primary account.
To ensure this doesn’t happen to you be sure to do the following:
1. enter your System Preferences through the Apple menu
2. Click “Accounts,” and make sure that the lock in the lower left corner is unlocked
3. Then click your “Guest” accounts and delete them using the minus button at the bottom of the pane.
And as always, use Time Machine. OR contact us so we can set you up with a good online backup solution.
There is more information available on these forums: