I don't wear glasses, but I've managed to damage my wife's glasses during training. She has mostly used contacts since. Seems like a great improvement, one less thing to worry about.
On a related not, I managed to dislodge my uke's glasses during my shodan exam. You can see him putting them off the training area at 7:00 here on the video:
http://www.youtube.com/watch?v=zwpm8...eature=related