Skype is Cheap/Free But It Can Slow Your Network.

If you have 10 people in your office, and they are using Skype did you know that Skype uses the free computing resources of your computer to process calls for those users in a peer-to-peer type model. Skype is free or very low cost, in fact I used it just yesterday to call friends in Uganda ($1 for 10 minutes!!!). However it can be a drag on your network.
Use Skype, but monitor how much of your network and computing resources it is using.
Information Week writes Skype is an unauthorized application,” said Chris King, product marketing manager at Blue Coat Systems whose ProxySG appliance can control Skype. “There are security issues, and there are network performance issues.”
Unlike the telecommunications companies that complain about the loss of revenue to Skype, IT and network managers are concerned more about security issues and network overloads, King said in an interview this week.
Unauthorized Skype traffic on enterprise networks “can use up chunks of bandwidth” when “supernodes” and routers are overwhelmed, the product marketing manager at Blue Coat said.

Learn more about Skype and Peer to Peer here
The University of Minnesota’s Safe Computing Web site reads Instances of Skype on the University network have been found to be the highest users of network resources. This is likely because the software can act as a Supernode. From the Skype privacy policy:
“A Supernode is a computer running Skype Software that has been automatically elevated to act as a hub. Supernodes may assist in helping other users to communicate or use the Skype Software efficiently. This may include the ability for your computer to help anonymously and securely facilitate communications between other users of the Skype software who, due to network and firewall constraints, cannot establish direct connections.”
Therefore, running Skype means your system can (and probably will) participate in providing Voice over IP (VoIP – internet phone calls) services outside of your direction and control. You are also agreeing to provide services to Skype for resources owned by the University. Individual users are not empowered to give such consent.

When you are not using Skype completely turn off the application. This way Skype will ONLY be in use when YOU need it and not consumer your network resources for others.