[drewblay]

>If I have 1.73 miles, I have to do the math to figure out how many feet that is, 1.73*5280~=9134, which is not something that's easy for me to do in my head.

How often do you need to do this in reality? Most people in their day-to-day have no need to these conversions.

[vladtaltos]

you should also consider the extensibility of the metric system as well. Any unit when has a kilo prefix is understood to be x1000 even if you are not familiar with the original quantity. kJ is kilo joules, km is kilo meters. I have no idea how this is handled in your non-metric system is but this property of the SI system definitely makes it much more extensible. you immediately get a sense of the ratio of different metrics. for example consider the ratios of miles/feet ??? feet/inch ??? (I have no idea) compared to kilometers/meters meters/millimeters... this makes it possible to define a metric for a quantity ( meters for distance for example ) and represent all the related quantities easily without having to define a new name for a constant multiple of that quantity.

of course perception of a metric also plays a tremendous role here. I don't have a 'feel' for how long it is 12-feet for example but I can eye-ball a distance and tell how many meters it is pretty accurately. I guess this perception is the main issue that prevents imperial system to be abandoned in favor of SI - people are too much used to it.

I also hate the left driving lane of UK btw. It screws up with my head every time I rent a car in London...

stupid metric-ism ;)

[raldi]

Whereas quite often you'll need to know how long it’s going to take to drive to a city 90 miles away, and it's quite convenient to use the "1 mile ~= 1 minute" approximation to estimate that it'll take 90 minutes.

[phlo]

And this is where metric really shines: at Autobahn speed (130 kph), 90 miles is only some 66 minutes -- 24 minutes saved over imperial. :)