At a recent vSphere troubleshooting class I taught, the break/fix lab which caused the most issues was an incorrectly configured service console port.
The esxcfg commands for this (i.e. esxcfg-vswif) are pretty well documented; however one nice tip that was successfully used in the graduation labs, was the use of the console-setup script.
Console-setup is a great menu driven script available from ESX 4.0 U2. It is accessed from the console of an ESX host machine and typing the command console-setup
This script will aid troubleshooting connectivity issues such as an incorrect IP address, or incorrect/missing vlan id for a service console port.
I have recorded a short video on how to use the command.