The next use of sniffing is for attack. This is how those aforementioned script kiddies use sniffing. Every successful military operation begins with good intelligence. Sniffing can get that good intelligence. It allows you to see what sort of services are being run on the target network, and it may allow you to harvest usernames and passwords. It can also be used to fingerprint operating systems ”to determine exactly what operating system is on a given host ”merely by examining which services (and which versions of those services) are active. Jose Nazario's paper on doing just that is at http://www.crimelabs.com/docs/passive.pdf .