Reading up on VMWare VSphere Virtualization

If you are learning about VSphere, here are the reference guides you should start reading:

Introduction to VMware vSphere
Getting Started with ESX
ESX and vCenter Server Installation Guide
Upgrade Guide (Updated 10/08/2010)
Datacenter Administration Guide
Virtual Machine Administration Guide (Updated 10/11/2010)
vSphere Web Access Administrator’s Guide
ESX Configuration Guide
Resource Management Guide
Availability Guide
Fibre Channel SAN Configuration Guide (Updated 10/08/2010)
iSCSI SAN Configuration Guide (Updated 10/08/2010)
Configuration Maximums for VMware vSphere 4.1

All docs can be found here: http://www.vmware.com/support/pubs/