This must be the most popular topic of conversation whenever a bunch of Europeans get together...
The U.S. adopted the English system of measures several hundred years ago and while the rest of the world (including Great Britain) moved on, going with the Metric system instead, we stuck with the good old pounds, inches, and ounces. As is the case whenever an entity used internationally lacks international standards, it's been causing loads of confusion and even disasters. Besides asking why this is so (the United States is uniquely insular in this respect, even more than actual islands such as Japan or Great Britain where such a thing would have a natural justification), a lot of people engage in the oft time-consuming and fruitless rhetoric of which system is superior. I'm going to add to this hairball, but only a little bit. And I'll try to use first principles rather than dogma (we'll see if I succeed).
The goal of having a standard of units are to provide a common framework for the society to efficiently and robustly (i.e. in a way that's resilient to errors) convey information about measures that doesn't require special skills (i.e. to make the framework usable by as many people as possible).
I think there are two factors one must take into consideration when comparing the two systems: the intrinsic properties of the units (how practical they are in daily use) and the way they can be manipulated and composed (how to multiply them, compare them, convert them). I claim that the Imperial system is superior at the former, and the Metric system--at the latter.
What makes Imperial units intrinsically superior is the very choice of how much a primitive of various frequently uses measures actually measures. I think an inch is superior to a (centi)meter -- I'm sure that if we were to take a survey of all lengths that humans refer to in their lives (controlling for a selection bias--people will tend to round up or down to the nearest unit of whatever system they are using), and draw a histogram of such usage, there would be a peak around the inch and not the (centi)meter. I'm even giving the Metric system the benefit of the uncertainty around which unit specifically should count as the primitive. In other words, we're more likely to talk about things which are the size of an inch than things which are the size of a centimeter. Similarly, the (mili)liter is inferior to a fluid ounce -- a fluid ounce is a more natural measure of a "splash" of a liquid.
There is a second-order effect of measures around, not at the primitive: do things more naturally come in (sub)harmonics of an inch ("half an inch"/"one-quarter of a pound"/"three ounces") or the meter ("three centimeters"/"one-half of a liter"). This is probably much harder to determine. However, one important property of the Imperial system is that it operates primarily on natural and not decimal fractions of units. The Metric system talks about 0.2 centimeters; the Imperial system talks about one-eighth of an inch. Natural fractions are (even by the very definition) more engrained in the human nature than decimal fractions--we're used to thinking about dividing things into equal parts and visualizing individual parts than dividing into a fixed number of parts (10) and visualizing multiples of that fraction.
The most important benefit of the Imperial system, in my view, is that it operates (mostly) on base 12 and not 10. I already wrote about how base 12 is far superior to base 10--it divides cleanly into 2, 3, 4 and 6. Base 10 numbers divide cleanly only into 2 and 5. Having intrinsically more divisors is better because it avoids awkward infinite fractions and, ultimately, inefficient communication.
When it comes to the second factor, though (how the units are manipulated and composed), the Metric system wins hands down. The Imperial system is inconsistent (12 inches to a foot; 16 ounces to a pound); there are far more units to remember (fluid ounce, pint, quart, gallon) and more units to remember the relationship between. The Imperial system captures many fewer measures at the very small and the very large range -- in fact, the only way to represent very small or very large numbers is to use the multipliers that are the very foundation of the Metric system (10 million pounds, for example)!
Most of the disagreement, then (especially when a bunch of Europeans get together...), can be boiled down the the philosophical difference (I define a "philosophical difference" as a difference in opinions that cannot be reconciled with logic because it's simply too costly to find a way to compare the opinions objectively) -- do you prefer the intrinsic properties of the units (which I feel are more aligned with human nature), or the composition properties of the units (which are more aligned with civilization).