Not sure if this is a real issue, but I was informed of the possibility that text fields on forms could pull data from SFDC when a lead that is already in our system encounters another form with the same text field option.
Perhaps there should be a way to block leads who encounter multiple forms with the same text field option from seeing what has been entered in the past, either by themselves with the initial form fill or via the entry of information by our own SFDC user.