This is a topic close to my heart, as a screw up by the CIC has delayed my receipt of my permanent resident card. It should be here by mid-December, but I am going to check with them by month's end just to be sure. I also plan to keep all my travel itineraries and boarding passes, as well as insist that the border control agents stamp my passport when I re-enter the country. I don't want there to be any doubt that I am meeting my residency requirement.
Read about what can happen when you don't meet the requirement in this article from The Toronto Star.