At least the whole EU uses SI units by Directive 80/181/EEC (so called "Units of Measure Directive"). From everything I know, most other countries of the world use SI as well. Not surprising, as the system is now 55 years old and explicitly replaced former definitions.
The Imperial volume units used in Britain are vaguely metric, and different from the US customary (i.e. Queen Anne) units. The Imperial gallon is the volume of 10 lb avoirdupois of water at s.t.p. The other similarity to French metric units is they replaced a number of different application-specific volume measures.
At about the same time as the Imperial unit reform Britain introduced the "florin" 2 shilling coin, 10 per pound, another vague attempt at decimalization.
>In 1981, the USMB reported to Congress that it lacked the clear Congressional mandate necessary to bring about national conversion. Because of this ineffectiveness and an effort of the Reagan administration — particularly from Lyn Nofziger's efforts (http://www.washingtonpost.com/wp-dyn/content/article/2006/03... ) as a White House advisor to the Reagan administration, to reduce federal spending — the USMB was disbanded in the autumn of 1982.
>The metrification assessment board existed from 1975 to 1982, ending when President Ronald Reagan abolished it, largely on the recommendation of Frank Mankiewicz and Lyn Nofziger. Overall, it made little impact on implementing the metric system in the United States.
>According to Mankiewicz, he prompted Lyn Nofziger's efforts to halt the 1970s U.S. metrication effort, who convinced President Ronald Reagan to shut down the United States Metric Board
> So, during that first year of Reagan's presidency, I sent Lyn another copy of a column I had written a few years before, attacking and satirizing the attempt by some organized do-gooders to inflict the metric system on Americans, a view of mine Lyn had enthusiastically endorsed. So, in 1981, when I reminded him that a commission actually existed to further the adoption of the metric system and the damage we both felt this could wreak on our country, Lyn went to work with material provided by each of us. He was able, he told me, to prevail on the president to dissolve the commission and make sure that, at least in the Reagan presidency, there would be no further effort to sell metric.
>It was a signal victory, but one which we recognized would have to be shared only between the two of us, lest public opinion once again began to head toward metrification.
The \N in 'NIST' is for "National" and the nation to which "national" refers is the United States. I'm not against switching to metric, but after forty years since I read about it in fourth grade, I am pretty confident that the switch won't make most people's lives better.
I don't think a good argument can be made for Celsius. Like Fahrenheit, Celsius exists as a measure of temperatures within the typical experience of humans. There is one primary use of such a scale, and that is measurement of air temperature (weather, indoor temperature). A distant secondary use is in cooking.
Faherenheit's 0-100 range is basically a close match for the extremes in weather temperature experienced by typical human beings. Celsius is not even close. Additionally, Fahrenheit's scale has roughly twice the resolution of Celsius, and humans are good at distinguishing this precision. Unit precision is also helpful for body temperature.
Regarding the distant secondary use: obviously Celsius's range matches freezing and boiling: but because water's phase change is consistent and obvious at these temperatures (modulo altitude), cooking rarely involves measuring temperatures in this range except for unusual cases like candy. Celsius has no advantage at all for the primary use of temperature in cooking: baking.
