v.2012/1
Wireshark is a FREE and open-source network analysis tool , downloaded over 500,000 times per month ! Along with the skills , and correct sniffing hardware - especially when it comes to wi-fi , you'll be able to capture and analyze all your network's traffic. This is the way to monitor your network at a low level and either fix problems or improve performance and stability - not to mention security related issues.
v.2012/1
The skill to "read" the network at packet level is becoming ever more valuable in a world with complicated networks and the possibilty of network exposure or failure. It is simply becoming necessary to record your network traffic in very much the same way companies record voice calls. This allows you to have a look at network issues , attacks or abuse after the fact - YES you can now see if a PC had a netbot virus or how much time a user spends on Facebook or listen to VOIP calls for quality or re-assemble a users downloaded pics or email. Wireshark is the most powerfull network analyzing tool on the planet and you need to know how to drill down into your network using it's tools.