From Microsoft:
Microsoft announced the release of Microsoft Desktop Optimization Pack (MDOP) 2009, which is available to customers with Software Assurance. Those customers can download MDOP on the Microsoft Volume Licensing Site (MVLS), and IT Pros needing to download for evaluation can access MDOP on the MSDN and TechNet sites.
This release includes updates to Application Virtualization (App-V), Microsoft Enterprise Desktop Virtualization (MED-V), and Microsoft Asset Inventory Service (AIS). You can read more about MDOP 2009 on the MDOP Team Blog.
Speaking of which...
MED-V provides deployment and management of virtual Windows desktops to enable key enterprise scenarios. MED-V 1.0 helps enterprises upgrade to the latest version of Windows even when some applications are not yet compatible. MED-V builds on top of Microsoft Virtual PC to run two operating systems on one device, adding virtual image delivery, policy-based provisioning and centralized management.
I've said this before, but let me say it again in one of those "mark my words" things: Seamless application virtualization, like that offered by MED-V, is the future of application compatibility in Windows. This will allow future Windows OSes to break from the past, compatibility-wise, because they'll be able to virtualize compatibility.