HTTP/1.1 200 OK
Knowing that this site is runing IIS 5 tells the potential cracker a lot about the OS that's runnning (i.e. Windows 2000) and therefore what attacks may work, or which do not work on that platform.
Port80's ServerMask product strips off the banners indicating what version of IIS you are running. Which in turn just adds another layer of protection to your defense in depth strategy.