i've only been across the border maybe 2 dozen times in my life (which is odd, since i live right next to canada) but i've never been denied entry, or pulled over and searched.......knock on wood.
only since 9/11 have i started to bring my birth certificate with me about every other time i cross. Seems whenever i dont' have it they ask for it....then give me a lecture about how a drivers liscense only sais that the state of michigan will let me drive and does not indicate that i am in fact a US citizen. But they always let me go.
Quis custodiet ipsos custodes (who will watch the watchmen?)