How Hard Is It To Leave The U.S. For Jobs?

Durrik asks: "There have been many articles and comments posted on how easy it is to move from Canada to the U.S. for engineering jobs. I'm one of the engineers that has picked up on this and left Canada for the U.S. for an embedded programming job. But now the high tech economy is heating up again in Canada and I want to take advantage of it, and I'm sure others do, too. Does anyone have any experience, and comments on leaving the U.S. for engineering jobs, or is this something so strange that no-one even thinks of doing it? What laws and trouble would I need to go through to go back to Canada, as a citizen? But since this is an open forum what about those who are U.S. citizens and want to take advantage of the heating up high tech industry in other countries? "