cyccommute 

Or, better yet, know a reasonable approximation. You hardly need to know that 37C is 98.6F. You only really need to know that 100F is around 40C. Same with distances. 12" is 1/3 of a yard and a yard is almost a meter so 1/3 of a meter is 30 cm. Good enough for most uses.

I did an organized tour this summer in Belgium and the Netherlands this summer. The tour leaders did a good job of giving both temperature and distance in both systems. However the 'Merikans on the trip had all kinds of troubles when they were away from the leaders. If they saw a temperature sign, they couldn't tell if the temperature was hot or cold. They were also using cue sheets that were marked in kilometers and were endlessly getting confused about the distance. After a couple of days of this, I gave a tutorial on how to navigate the metric system. All you really have to remember about temperature is that 20C is about room temperature and 37C is body temperature. If you are riding and you see a thermometer that says 30, it's a warm day. If the thermometer says 40, it's hot.

For distance, our cue sheets said things like "0.1 Turn left" and "1.6 km Bear right at small church". A tenth of a kilometer isn't a tenth of a mile. It's only 100 meters or 300 feet. 300 feet is a US city block so the turn is right now! (0.1mile is 528 feet, almost twice the distance) and 1.6 km is about a mile.

Once people got the ranges in their heads, they could use them to estimate the measurements which is all that is really needed.

And, yes, Google works for all kinds of measurements.