Note: Microsoft announced the new licensing for Windows Server 2012 since this post. Check out the licensing scenarios here. And note that Hyper-V is free anyway if you are legally licensing your Windows Server VMs. Hyper-V Server has a place, but usually not when running Windows Server VMs.
I was downloading some stuff from TechNet for the lab at home when I noticed this:
In fact, I nearly accidentally downloaded it … ick! 
I didn’t read anything about this release at all.
Hyper-V Server is the free to download hypervisor from Microsoft. Licensing-wise, it has a teeny tiny niche market. That’s because you never license VMs for Windows Server, even with VMware or XenServer; you license hosts with Standard (usually SBS Premium), Enterprise (very small site), or Datacenter (makes sense financially with around 7 or more VMs per host). And if you license the host + VMs with one of those, then you might as well use it. I prefer the full install, even in WS2012, and others who like Core can flip back/forth to the GUI in WS2012.
Where Hyper-V Server does have a place is:
- VDI: where you’re not licensing the host for Windows Server VMs. It might be pointless buying Datacenter edition when those licensing benefits are going to waste and not cancelling out the cost of the host OS. the free Hyper-V Server has all the same functionality.
- Linux VMs: Same argument as with VDI.
- You don’t have licensing for Windows Server, you want to build a host once, and play with downloaded time-bombed demo stuff.
Maybe you’re in that market for Hyper-V Server? If so, go grab the RC and start playing and learning.
EDIT#1
As soon as I post this, I see tweets that it’s just been announced at TechEd 
It will continue to match the Datacenter edition for features by the looks of the tweets.
EDIT#2
Oh for the hell of it, let’s have a look at the ESXi free edition comparison, courtesy of a tweet by David Davis:
Another obvious area would be if you want hyper-v 3.0 features but have licensed your vms for 2008r2…
Good one!
Why can’t you license the VMs individually?
You never license VMs. Any license you buy is assigned to tin. You can buy 100 Standards and use the “+1 for a VM on that host” benefit to license 100 VMs on a host (Hyper-V, VMware, Xen, whatever). BUT … you can only move those licenses once every 90 days (vMotion, Live Migration, HA, failover, etc). And you’ve just thrown away thousands of $£€ of your employer’s/client’s money. License the host with Enterprise/Datacenter. That gives you 4/unlimited rights for Windows Server licenses for VMs on that host and deals with the mobility issue. This has been the way since 2004. There’s absolutely nothing new about it.