Here at TechEd 2012 Microsoft has released the Release Candidate for the standalone version of Hyper-V v3. This is considered the release that will be on par, or surpass, vSphere. You can download the RC version from Microsoft's website at http://www.microsoft.com/en-us/server-cloud/hyper-v-server/default.aspx.
Hyper-V v3 has doubled the capacity of v2 with logical processors supported per host have gone from 160 to 320; physical memory from 2 to 4 TB; and virtual CPUs from 1024 to 2048. Virtual CPUs supported per VM have also doubled from 32 to 64.
Now I don't know anybody that would even think about running a VM that large on Hyper-V. I have some playing around to do, but I don't think Hyper-V is ready for primetime workloads like vSphere is capable of. vSphere has the history, experience and respect to support critical workloads. Not to mention you'll have to patch your Hyper-V server every black Tuesday (or shortly thereafter).
I'll definitely load up Hyper-V v3 in my lab and take it for a spin. I need to get my VMM server up and running too to be able to take full advantage. Does anybody know if VMM 2012 supports Hyper-V v3? Now for some more homework.