Having lived well over a decade in the country that founded the metric system, or the SI (Système internationale d'unités), I do now think in terms of kilograms and litres and metres, but I can't say that I find the system more useful. Logical, Cartesian, yes obviously, but practical and intuitive, even elegant? Certainly not.
US Customary and English Imperial measures—the pound, the gallon, the yard—grew organically from usage and were refined with practicality foremost in mind, and their hallmark is units that are intuitively proportional: 16 ounces to the pound, four quarts to the gallon, twelve inches to the foot and three feet to the yard. The decimal-based metric system replaces all this with measures of technocratic precision, mathematical logic and an appeal to universality.
The English-speaking world has in part resisted this appeal to universality and often countries have retained their traditional weights and measures in parallel with their metric equivalents. Though Britain itself began conversion in 1995, certain defining measures remain unchanged: by law, beer can only be sold in pints and road signs can only record distance in miles. The metric system remains largely foreign in everyday use in the US, and as one who is constantly measuring and designing, I believe this to be a good thing, for the traditional foot is an extraordinarily powerful design tool, one whose innate proportions are unconsciously absorbed by native-born designers, enriching and supporting the process of creation.
The same intuitively occurs when designing just about anything of human scale for human use, and really this is quite obvious to anyone using the inch/foot—it is a supremely elegant proportional system as much as it is a unit of measure, and therein lies its beauty, its utility and its genius.
Our forebears (going all the way back to the ancients themselves, whose geometry was proportionally based) all knew this, and when Renaissance architects began to publish elevational drawings of ancient architectural elements, their measures were usually given in fractions/proportions, not in the units of any particular system of measurement. Indeed, the standard unit of measurement of the columnar orders is a column's diameter at its base; the "standard" shaft of a Doric column is 8 diameters high; the Ionic, nine, and so on. (At top, Palladio's elevation of the Doric order, from his Four Books.)
In the Age of Reason, French surveyors made a grandiose attempt to accurately survey a meridian arc so as to precisely calculate the new metre (defined technically as one-ten millionth of the Earth's meridian along a quadrant and poetically by Condorcet as "for all people for all time") which was to replace the venerable toise (defined by edict of Charlemagne in 790 as the distance between the fingertips of a man's outstretched arms, and in practice roughly equal to the English fathom, or six feet). The surveyors ran into some difficult terrain, causing them to fudge mightily, and so the new metre came up short by 1/5 of a millimetre per metre when all calculations were tallied and decimal points placed. The metre had already become well established when this came to light and consequently the error was never corrected, and so it is that today the earth's circumference measures 40,007,863 metres, not 40,000,000.
So much for technocratic precision and mathematical logic.
In practice, designing with the metric system is often tedious and unsatisfying. A chore, frankly, like anything arbitrary and imposed. Good design is underpinned by rhythms, convergences, and harmonies, and the simple decimal divisions of a metric ruler demand that those elements be calculated and plotted out quite laboriously, ex nihilo. Imagine scrapping musical notation for herz impulses per second and you have a rather good approximation of the practicality of the metre as a compositional or design tool.
Which reminds me of a certain well-known and quite imperious German architect who was obsessed by the square and the grid and who made van der Rohe look like a free spirit (well this is not so unusual; German designers are often seduced by the square and the grid, just as many French designers are enamored by the poetry of the arc in tension, as a quick flip though any German or French design magazine will illustrate). Anyway, in his last years this architect received a prominent commission for a museum of contemporary art and based his entire design upon the square. Square windows, cubic rooms, grids everywhere—an orgy of order!
His obsession went so far that he designed square-sectioned stairs—rise over run equal, making a perfectly diagonal flight. Perfect order, and perfectly disastrous. He ignored all protestations of impracticality and even danger—for as (almost) any architect knows, you don't go about reimagining the proportions of stairs every Monday morning on a whim; there are well-defined standards that are employed unquestioningly because they have been optimized for the body's movement and refined from vast experience. Long story short, the building opened and the stairs were swiftly condemned before someone was actually killed trying to use them. It is hard to conceive such folly occurring in a mind conditioned by fractions and proportions, rather than the arbitrary tyranny of the decimal point.
