I have a rule about street musicians. If they make me smile, I give them money. And that goes for subway musicians, too.
Last weekend, when I got off the C train at the Museum of Natural History, the last thing I expected was to find a man sitting in the subway station, playing a kokyu (at least I think that's it was). He got money. The roving mariachi bands that invade subway cars with carefully-engineered choruses of "Cielito Lindo" that leave just enough time to pass the hat before the next stop -- if they're engaging -- and their instruments are in tune -- they get money.
One bleak evening last winter, there was a little black cloud over my head until the subway doors opened on a spirited Celtic fiddler, blonde ponytail bobbing in time to the music. I quickly rummaged in my purse for a handful of change, took careful aim, and tossed it onto the platform before the doors closed again. Money well deserved.