The United States has officially recognized and endorsed the use of the metric system (officially the International System of Units - Le Système International d'Unités - or SI) since 1866. However, it is one of three countries in the world that has not adopted it as its primary system of measurement (the other two are Liberia - a former US colony - and Myanmar).
This is not a post about how great the metric system is (very great), or why the metric system is better than the conventional system (it just is), or even how stupid the US is for refusing to adopt such a common sense series of units (quite stupid). No, this post is none of these things because all of these things have been written about ad nauseam.
Essentially, the United States has refused to switch to the metric system because of a myriad of political and cultural reasons. It is the only developed country in the world that has continued to use conventional units (with the quasi-exception of the UK), and most people tend to believe that metric units will continue to be used only in academia and technical fields like robotics and engineering. However, I believe that the US could, and will, switch much faster, and much sooner, than is presently predicted. And all because of the Internet.
North America has the highest percentage of Internet penetration in the world (73%); the United States alone has about 220 million Internet users. Internet culture has blended so much with American culture that it is not uncommon to hear Internet expressions like "lol" or "1337" (pronounced "leet" and short for "elite" for all you non-1337 h4x0rz out there) used in everyday verbal conversations. The Internet also uses metric.
Think about it; the hard drive in the computer you are reading this on is measured in gigabytes, the SI prefix giga, meaning "one billion," bytes. My Internet connection is measured in Mbps - megabits per second (mega being the SI prefix for "one million"). The resolution of the photos you uploaded to Facebook the other day are measured in megapixels. You use the metric system every day on a computer and on the Internet.
The international nature of the Internet also contributes to the metric influence. Since so many (metric) countries are represented on the Internet, and since the Internet hosts content from all of them, it is inevitable that if one spends enough time on the Internet, one will encounter the metric system.
It is this subtle infiltration of America by the metric system that I believe will ultimately lead to a United States in line (literally) with the rest of the world. 90% of US residents aged 18-29 use the Internet, and so the metric system has finally learned what the Catholic Church has long known - "get 'em while they're young." I foresee a kind of Glorious Revolution in which the metric system is finally introduced, in policy, as the primary system of measurement for the United States by the maturing Internet-age of Americans - those born 1992 (the birth of the World Wide Web) and later.
Gone will be the Carter-era pamphlets on "metrication" and a "metric future," to be replaced by...well, nothing. We don't need propaganda to convince us to use the metric system, we already use it voluntarily with our computers and the Internet. The Internet has brought the world together, and has (recently) begun the process of standardizing a compendium of knowledge and experience (including a system of measurement) that transcends national boundaries. As high technology becomes more and more integrated within our culture, the metric system, the measurement scheme of high tech, will become integrated, as well.
Fear not the revolution, for it has already come.
P.S. Commenter Dr. Detroit makes a very good point, and I am reproducing part of his comment here:
"There were many starts and fits in the direction of the metric system in the US since the fateful year of 1866 when it became legal throughout the land. A toxic combination of business lobbies (it's too expensive!), undereducated patriots (it's un-Amerikun!), and sheer inertia (imperial works, why bother?) has killed off any serious attempts at conversion several times. Although people may know their kilo-, mega-, and giga- prefixes thanks to PC's and the Internet, we still live in an America of 21-inch monitors, 3.5-inch hard drive bays, and hard-drive densities measured in bits/square inch."
It is, sadly, true that high technology, because much of it is developed in America, is subject to the awkward dual use of metric and customary units. I would concede the point that many measurements of high-tech devices are still measured in inches and other imperial units. However, it is conceivable that we are in the first stages of a metric transformation that could be graphed as a parabola, that is, a transformation that starts slowly but builds upon itself to become a huge and significant force within a short period of time. As the generations that never learned the metric system age (or as my mom so eloquently put it to me, "when I die"), the metric system may gain ground at an exponential rate (hence the parabola comparison). Already we are seeing some small glimmers of hope as computer manufacturers have completely rejected the idea of using fractions of an inch in screen size measurements, in favor of the decimal system (ie .1, .2, .3, etc.) which is used by the SI.