Don't have to "sneak" in. My family and I returned from a trip to Costa Rica in January of 2003. Our flight originated in Costa Rica and we changed planes in Guatamala and then on to Dallas. At the Dallas immigration we, and the rest of several plane loads from South America, were waved through. They asked us if we had purchased anything and on we, and everyone else, went on our way. I'm not even back in the US according to my passport.
How's that for security?
They only check us in the US where I had to remove my shoes and have all my baggage emptied.
Boy, you can tell the feds are taking this very seriously....