The Nmap Security Scanner was built to efficiently scan large networks, but Nmap's author Fyodor took this to a new level by scanning millions of Internet hosts as part of the Worldscan project. He presents the most interesting findings and empirical statistics from these scans, along with practical advice for improving your own scan performance. An overview of new Nmap features is also provided, including the Nmap Scripting Engine, Zenmap UI, new performance options, Ncat, and Ndiff. Most of these are now available in Nmap 4.75.
For more, see http://insecure.org/presentations/