Typical Windows shop will automatically favor the Microsoft alternative to any technology available. It's a automatic and ingrained into their 'IT' psychological makeup.
So despite the fact that Hyper-V is inferior to solutions like Xen, Linux-KVM, or anything out of Vmware it does not really matter. Since it has the 'Microsoft' name, it integrates into Active Directory and into Windows Server it will automatically become very popular.
This is a big step forward for Microsoft. Not only is it GPLv2 code coming out of Microsoft it should massively improve the performance and integration when running Linux systems in Hyper-V and make it just that much cheaper and easier for people to start using Linux at their businesses*.
* that is unless the anti-M$ brigade comes out and makes enough fuss that it gets stripped out of the kernels in distros because of vague worries about unspecified patent threats.