Then hopefully you are not a dual citizen. News reports say over a million of them stand to be hounded in Canada by the US IRS. Even the Harper Government is complaining! They have a mighty long arm!
There is a way out, but they make it as difficult as they possibly can:
http://travel.state.gov/law/citizenship/citizenship_776.html
and your troubles don't end there:
http://harpers.org/archive/2004/10/0080240
You gotta love the irony. A nation founded on the principle of "no taxation without representation." What a laff.
ebear