Your Face Is Not a Bar Code
Phil Agre has a solid essay opposing automatic face recognition systems in public areas. These uses are only going to increase, because the technology is cheap (enough) and appealing to authorities everywhere; it's good to have some arguments to hand for opposing the spread of the cameras.
Or sure, you won't look suspicious wearing a Superman mask or covering your face the entire time you're talking to a salesperson. Seriously, if you came into my bank wearing a mask of any kind, I'm hitting the panic button before you can say anything.