No, I have never had so much traffic happen that my site has gone down because of it. If I did I would probably have seen it as an achievement, to be honest at first. It would mean I was doing something right I guess if my site went down due to traffic. Only time I have known my site to go down was if the hosting service I was using had issues and they were usually really got at alerting me to any issues there would be so I could let my members know before hand.