I do contract work for a major ISP and you would be amazed at how many DDoS attacks happen on a regular basis....yes, they are traceable, but it can be very time consuming depending on the level of knowledge that the twit has. Fro the most part, the attacks that I've backtraced have been out of places like Bolivia, Russia, Taiwan and are not really feasable to pursue, so they end up getting away with it. We just take the hit on our routers and they eventually go away.