Desktop Virtualization doesn't just mean using your existing server virtualization platform to deliver virtual desktops. As many people have found out, the ROI on doing this for a mass VDI solution doesn't stack up.
If you take a user centric approach to defining the requirements, you should end up focusing on the user Data and Applications rather than the platform on which you will run the OS.
I see a new lease of life for Windows Terminal Services, now called Remote Desktop Services (RDS) in Windows Server 2008 R2. If you have not evaluated RDS and only had experience with TS then I would encourage you to look again at the Microsoft offering. There are many architectural changes to have resolved many of the issues previously experienced with TS. e.g.
· 64 bit only - better concurrent session support
· Integration with System Center and Unified Access Gateway - manage in the same way as physical desktops
· Application Virtualization - less susceptible to dependencies allowing greater number off apps per server and easier updates
Microsoft virtualization strategy http://www.microsoft.com/virtualization/en/us/default.aspx
RDS Component Architecture