I love the metric system for its obvious simplicity (1 meter = 100 centimeters) and elegance (one liter of water weighs one kilogram; one cubic meter of water weights one ton, or 1,000 kg).
In the Netherlands, I enjoyed the metric system in its full glory, and I thought I was going to have the same experience in Canada, but I am not.
Before Canada started switching to the metric system in the 1970s, it had a system that borrowed elements from the UK and the US. That system was confusing (e.g., an imperial gallon is 4.55 liters; a US gallon is 3.78 liters), and so it made sense to move to a single, logical system such as the metric system.
But the switch didn't exactly occur, and Canadians today use pounds and feet, alongside kilograms and meters. In some ways, Canadians are in an even worse situation than Americans, who've firmly rejected the metric system (except for kilos of cocaine and two liter bottles of coca cola). This confusion increases transaction costs, as people need to find or convert to a common unit of measure (I'm trying to sell a backpack that has 65L/4,000 in3 of capacity, telling people that I am 1.78m/5'10").
Transaction costs do not just affect communication among people; they also slow down our internal thinking, by forcing us to convert measures or -- worse -- ignore measures in our everyday affairs.* I blame some share of American innumeracy on our chaotic system of measures, which means that Americans make more gratuitous mistakes. It seems that Canadians are handicapping themselves in the same way. That's a pity.
Bottom Line: The metric system makes it easier to measure and relate different objects and ideas. Those who do not use it cannot think as clearly as those who do.
* The same holds for tipping and sales taxes here. In the Netherlands, people do not tip. Service is still good since servers are paid a good wage. Taxes are included in the price (e.g., €1.99 means €1.99) but you can see them on the receipt. It's silly to sell something for $9.99, then ask someone for $11.20 here (12% tax). Just tell me the price; don't make me THINK even more about something I already decided to buy!