Using Euro coins as weights (2004)

At one point, I worked out that US dimes, quarters, and half dollars all weigh $20/lb (iirc), which made the task of counting my accumulated change a lot easier.

That's because that was the price of silver. The mint was for many centuries a way to get your precious metals divided into units of standardized weights that were stamped to certify their authenticity, thus facilitating commerce, though frequently rulers succumbed to the temptation of "debasing" them by diluting the precious metals with so-called "base" (in the sense of "low", "contemptible") metals such as tin, lead, and zinc.

So quarters weren't worth 25¢ because the government said so; they were worth 25¢ because they were made out of 25¢ worth of silver.

That's the same reason "peso" means "weight" and the "shekel" and "pound" take their name from units of weight.

This ended in 01965 in the USA, followed by the end of the gold standard, since which the dollar has lost 96% of its value relative to the precious metals that used to define it. The consensus among economists is that this is a good thing because it prevents deflation. I'm not sure.

Off topic, but may I ask why you use a leading zero when writing the year? (01965 rather than 1965)

You're not the only person I've seen do it on this site, and I can't recall ever seeing it not on this site, so I'm wondering if its because you're in the habit (or wanting to be in the habit) for some technical thing you do like working on a database that needs years in that format, or if there's some reason you feel that its better to write them that way in prose?