Fun, but if you have a managed switch, there are some even more interesting things you can do, like bandwidth monitoring:

nTop - http://www.ntop.org/news.php

And realtime traffic stats:

http://iptraf.seul.org/

If you run SIP on your network, you can capture call setup information to debug phone issues:

http://wiki.wireshark.org/SIP

And even extract RTP audio streams to investigate call quality issues:

http://wiki.wireshark.org/RTP_statistics