Finally, Hyper-V is coming to Windows client and not just server. For a long time I have to use 3rd party products such as VirtualBox, which is very nice, or VMWare Workstation, etc. to run my 64 bit VMs or dual boot to Windows Server instance to try out Hyper-V. Guess it's no longer required since Hyper-V will be built-in to Windows client itself.
Mounting VHD is also easier to do in Win8 (at least from what I've seen in the keynote).
Another cool thing is mounting ISO is also easier now and built-in to the OS.