vSphere 4 Editions: Core Platforms

This matrix highlights the differing Editions and Pricing and prices of Vmware vSphere 4:

• Thin Provisioning is native to vSphere vCenter, not ESX. ESX/ESXi 3.5 can run witth Thin Provisioned virtual disks (VMDK).
• Storage vMotion is now NATIVE to the client interface (no more 3rd party plugin). Right-click, migrate, wizard walk, and your done.
• Very Important! FaultTolerence - Vmware says, "VMware Fault Tolerance is supported with virtual machines with only a single virtual processor. VMware Fault Tolerance ... requires at a minimum the Intel 31xx, 33xx, 52xx, 54xx, 74xx or AMD 13xx, 23xx, 83xx series of processors; and works with any future generation of these processors."
  

Before you expand your virtual infrastructure with new servers, make sure you're buying the correct supported processors Fault Tolerence is desired.