A few years ago Air Canada offered a new trial product: unlimited-travel flight passes. If you were willing to limit your travel to a small region, you could get one for only a few thousand dollars. Some enterprising individuals picked these up and proceeded to take as many as a dozen flights per day on short-hop routes... racking up frequent flyer points for every flight.

Six months later, the unlimited-travel flight passes were introduced as a permanent addition to Air Canada's travel options, with one slight tweak: You now get a fixed number of frequent flyer points per month, independent of how many flights you take.