Lots of conversations in the booth today about securing VMs running on Windows Server 2008. And the conversation always revolves around best practices to secure your Windows Server. Good processes and practices in the physical world are also good in the virtual world. Example, WSUS and WU will update OS and apps running in VMs, just like they do when not in VMs. But unlike 1 app to 1 server deployments where you could pull the plug if all else fails, when you're running 10:1 VM ratios, pulling the plug is out of the question.
Microsoft's Brandon Baker was recently interviewed on this topic and the article posted today in Dark Reading's web site. Given it a read and expect to see more content on TechNet on this topic.