The storage provisioned to the VMware vSphere environment is one area that I frequently clean up. It can be easy targets (such as powered off virtual machines that haven’t been used in a long time), or it can be less obvious things (such as a copy of a single VMDK file that wasn’t attached to an inventoried virtual machine).
One area that takes a little more work to clean up is VMware vStorage Virtual Machine File System (VMFS) version assignments on a datastore. Each version of vSphere Hypervisor (ESXi) will have a default format version for a VMFS datastore. The current releases of vSphere 4.1 format datastores at VMFS 3.46; the base release of vSphere 4 formatted at 3.33; Virtual Infrastructure 3 formatted at version 3.31 for ESXi 3.5; and ESX 3.0 systems formatted at 3.21.