Here are some of the features that are supported for virtualized environments.
- Presence
- IM (including remote access, federation, and Public IM Connectivity)
- Group Chat
- SQL Server back-end server
Check the full post over at OCSpedia.com http://www.ocspedia.com/Misc/OCS_Virtualization_Support.htm
Check out the supported server role collocation http://technet.microsoft.com/hi-in/library/dd425201(en-us,office.13).aspx
msunified.net 
Unfortunately, it’s not quite as simple. While Presence can be virtualised, it’s only the Front End server that is supported. Thus the main supported OCS architectures (Standard, and Enterprise/Consolidated) are NOT supported. This seems a tad surprising – the most popular deployment scenairos are NOT supported for virtualisation. There are, of course good reasons (aka quality issues) why some parts of OCS are not supported in a virtual environment, but it’s still a tad confusing for customers.
Thanks for your input Thomas! You are absolutely right about it not being simple. Bottom line is that all roles that have something to do with audio and video are not supported as virtualized server roles. So in a consolidated deployment there is not much that actually can be virtualized.