Just some brain storming to make the endless waiting less painful.
One way to notice the difference is to drive across border to the US. For Canadian or US citizens, one usually doesn't have to get off from the car; as other passport holders, including Australian and British, one has to get off the car, entering the document control, fill some forms and pay some bucks.
Another way is to go somewhere but transit via US. On the way back, Canadian citizens can use the lanes for US citizens which is way shorter than lanes for foreigners.
Of course, if you are already a NEXUS holder, you will see no difference in either of above.