Our admittedly small in-house virtualization setup started with two standalone ESXi hosts, one 5.0, one 5.1. Both in production, no feature licensing, so I basically had to shut everything down to do ...
One of the most lauded features of vSphere 4.1 is the built-in Active Directory authentication engine for ESXi hosts. It's very easy to configure, and it works for both free ESXi installations as well ...
We need to do a VMware consolidation down from 4.0 Enterprise to 5.1 Essentials Plus. I have 4 hosts that are going to be retired as part of the migration but I need to get the VMs off of them first.