"VMware would like to announce the availability of a public draft for the vSphere 4.0 Security Hardening Guide. This guide represents a new approach to providing security guidance from VMware."
A direct link to the guidelines can be found here: http://communities.vmware.com/community/vmtn/general/security?view=docum...
I would highly recommend reading these guides for your VMWare deployment. There are tips and techniques that could help you create a more secure cloud computing environment.