This thread is especially interesting to me because I suffer (really suffer!) from migraines. With a full blown migraine, there would be no question of me playing. I couldn't function at all. I'd be lucky if I were able to make a few last minute phone calls. One time I had a gig when I was on the tail end of a week long migraine. There were 11 others in the band, so I went and played as best I could and kept silent or droned when the going got rough. If I were the main act, considerations would be very different. I agree that giving a bad performance is worse than cancelling.