One of the most ridiculous things that Microsoft are saying as of late is that the feature in vSphere that allows you to over commit memory, is not such a big thing and that most people do not use it anyway - here here and here.
If you saw my previous post you will see that I managed to double the amount of virtual machines running on the same host (from 8 to 16 VM's running Windows 2003 Server 1GB RAM) without changing the 8GB RAM configuration on the host.
Would I be able to do this with Hyper-V? Hell No!
So I will say this again to Microsoft. Customers use Memory over-commit, they use it daily, and use it all the time. As long as you do not have this feature - this will be a strong point against using your product.
Enough said about that!