VMware orientated people know the VMware update manager. With this tool/plug-in in vCenter you can automate patch management of VMware ESX hosts and virtual machines which eliminate manual tracking and patching. This also works for offline virtual machines. For Hyper-v Microsoft got the Virtual Machine Servicing Tool (VMST) which works in combination with WSUS or SCCM to get the same result.
A read a article of the VMST 3.0 version of the tool. This version is still in beta so maybe some futures will disappear in the final version. The current version 2.1 this tested guidance and automated tools let you service offline virtual machines in your SCVMM library. The new, still in beta, 3.0 version adds some powerful functions. Functions that already exist on a VMware platform. Then new functions are designed to streamline the process of keeping your offline virtual machines, templates and VHDs up-to-date with the latest operating system and application updates. VMST 3.0 helps you manage updating your offline virtual machines according to their needs. When using VMST 3.0, you can live migrate the virtual machines within a cluster to another host so the there may be maintenance on the physical host. All this can be done automatically. The only think i am missing is the opportunity to make a snapshot before patching a virtual machine. Maybe i missed that with ready the articles . VMware has the same opportunities (and more) for some time now and is at version 4.0 update 1 patch 1.
For a VMware administrator with some history I though how did we accomplished that without update manager? It is great to see opponents trying to catch-up. I am curious what will be the answer of VMware, what more do we want form a update manager?
Info about VMware Update manager