I'm just going to quote my Slashdot post inline.. check out the links for all the nitty gritty details. The bottom line is that 5.00 is awesome, and includes everything I've written as yet -- download it! :)
The long-awaited Nmap Security Scanner version 5.00 was just released (download)! This marks the most important release since 1997, and is a huge step in Nmap's evolution from a simple port scanner to an all-around security and networking tool suite. Significant performance improvements were made, and dozens of scripts were added. For example, Nmap can now log into Windows and perform local checks (PDF), including Conficker detection. New tools included in 5.00 are Ncat, a modern reimplementation of Netcat (with IPv6, SSL, NAT traversal, port redirection, and more!), and Ndiff, for quickly comparing scan results. Other tools are in the works for future releases, but we're still waiting for them to add email and ftp clients so we can finally get off Emacs!