Version 2.0.2 of Pidgin allows usage of the Bonjour protocol. In order for the option to display in the protocols dropdown however you must install the Bonjour for Windows application which is freely available from Apple here.

Q and A:
Q. What is Bonjour?
A. Bonjour, also known as zero-configuration networking, enables automatic discovery of computers, devices, and services on IP networks. Bonjour uses industry standard IP protocols to allow devices to automatically discover each other without the need to enter IP addresses or configure DNS servers.

You can also utilize Bonjour as an "internal network chat", which will allow users within the network to talk to eachother without requiring an external server (such as AIM, ICQ, IRC, MSN, Jabber, etc).

The benefit here would be, if your network where to be down, you can still message inbetween computers for productivity.