In April VMware released their hardening guide for vSphere 4.1 (http://communities.vmware.com/docs/DOC-15413) , now the have also released a free tool to check your vSphere installations against their hardening guidelines.

The tool is called “VMware Compliance Checker for vSphere” – http://www.vmware.com/products/datacenter-virtualization/vsphere-compliance-checker/overview.html