As far as I can remember, I've only ever rage quit three times in the entirety of my online gaming experience. Once, years ago in a game of Counter-Strike: Source wherein I was actually doing quite well. However, the server admin didn't take kindly to my whooping his ass so he kept slapping me when I would, say, try to snipe or kept changing my name to some derogatory term. The second and third times were in Left 4 Dead and Left 4 Dead 2, respectively. Both times involved games of versus against teams that consistently used every damn cheap trick, glitch, and exploit in the book.
However, I've lost count of the number of times I've made an opposing team rage-quit in Left 4 Dead 2, let alone any other online game. Most people just can't handle losing.