After helping me to-

Diagnose a UDP/TCP issue when setting up our SIP trunk
Diagnose issues with a web page not going through our proxy correctly
Setup WoL in SCCM 2012 by working out how the packets were crossing the VLANs and identifying that the issue was with the weird Dell BIOS
Figure out which DNS addresses that the new SMARTNotebook software uses and allowing them unauthenticated through our proxy

I declare today a completely unofficial Wireshark appreciation day!
So any other stories people have to tell about how Wireshark has helped them?