Paddy-Pilot - yeah Canadians are still subject to tax, even when working offshore, so long as they are still deemed residents of Canada for the 6 months they are off work. Otherwise they could relocate to Dubai or some other tax free state in order not to pay taxes.
However, in Ireland, so long as you are not in the country for 181 days you are deemed a non-resident and therefore not charged any taxes. You can still own a home in Ireland and live there for the other half of the year and not pay income taxes - but as you may know in the wonderfully changing economy they are trying to change these laws.
Americans have it pretty bad, they have to file and pay taxes no matter where they live in the world for their life. I think though, if they are living outside the U.S., they are only hit with income taxes once earning something like $90,000 and up. Moral of the story, never be in too much of a hurry to win a green card or get US citizenship.