I had three different piano teachers growing up, and none of them, thankfully, were metronome fascists; the few times I tried playing with a metronome I found it fantastically stressful. It was like trying to write poetry while watching 24. (Not that I ever wrote poetry, nor was 24 around when I was growing up. But anyway.)
The metronome, though, made a name and a fortune for its inventor Johann Maelzel. (Well, actually, Maelzel made a name for himself wheeling around his "robotic" chess player The Turk, a story that still gets dredged up every few years for a new magazine piece—most recently by Adam Gopnik on the BBC. But the metronome didn't hurt.) Maelzel patented the invention in 1816, and even today "M.M." (for "Maelzel's Metronome") is used to notate tempo.
Actually, though, according to my Word of the Day calendar for yesterday, Maelzel didn't really invent the metronome—he just modified the design ever so slightly from a poor sap who hadn't thought to patent it himself. (One of his... con-tempo-raries?)
I bring this up not for any profound reason, but because the name of the original inventor was Dietrich Winkel. And the only thing I could think of, when I read that, was: Hmmm... That's weird. Turns out that if your surname starts with Winkel, you're pretty much doomed to have someone take your great idea and change the world with it.
The moral of the story? Buy Bitcoin instead.