Though I've had a nasty experience at Canadian immigration. Once I was invited to speak at a University of Ottawa law school event but neglected to bring the invitation letter. I was directed to secondary screening and spent what seemed like hours there before being allowed to enter the country. At one point a Canadian immigration official said they couldn't find any record of the conference, but as far as I could tell they were looking at the main school's web site, not the law school's. Sigh. Ironically the event was sponsored by the Canadian federal government...
At least it wasn't 33 hours of hell.