There are some who argue that Beethoven's metronome was broken, and his deafness was part of the reason he didn't realize it. Here's an article about it: http://www.nytimes.com/1987/02/19/arts/critic-s-notebook-pon...

Along those lines, John Eliot Gardiner conducted Beethoven's 9 Symphonies with Beethoven's metronome markings and with instruments that would have been used at that time period. It's a very different sound that I'm a huge fan of, though I think it wasn't particularly embraced by traditionalists.