Guys, just FYI, if you are dual citizen, like Iranian/Canadian, (even if you have burnt your iranian passport) you are not allowed to enter US. I know of few friends who were turned back at the border last night, with Canadian passport, however, their place of birth is iran, so the officer told them, you are still Iranian.
If you are working in US with Canadian passport and GreenCard, i strongly recommend you do NOT leave the country.