A great point made in a conversation I had with LiveLife8072 and NegationofP is that believers don't act like God is there, watching them. They act appropriately when someone real walks in and catches them in an uncompromising situation, like masturbating or something, but God was already supposed to be there. Perhaps this is a sign that, deep down, they don't truly believe.
"Every breath you take...every move you make...every bond you break...every step you take...I'll be watching you." ~ God (and Sting)