Joe Holland has just posted his first (but hopefully not the last!) document How to configure ESXi to shutdown using an APC SmartUPS.
His introduction says it all:
This tutorial will show you how to configure a VMWare ESXi install to shutdown using an APC SmartUPS. This proven practice came about because our company was sending a Dell PowerEdge T300 server with ESXi and a APC UPS to one of our sales offices. Because it would just be this server and the UPS there, we needed a way for ESXi to shutdown the guest operating systems and then itself gracefully.
Welcome, Joseph!