this is a “WOW” feature for me that I found not to be documented. Until now you could only “Import” a VM that you had previously exported.
Importing a VM from just a copy of the directory was not possible, and manual steps where not easy. See http://blogs.msdn.com/b/robertvi/archive/2008/12/19/howto-manually-add-a-vm-configuration-to-hyper-v.aspx
Now, Windows 8 Hyper-V simply allows that you point the Import to a existing VM folder. with your xml, vhd, avhd files.
Select if you intend to keep the VM unique.
In my case Machine Config (XML) and VHDs are in the same location, but the import process gives you a chance to select the VHD location
That even works for snapshots. Existing saved states are not compatible across Hyper-V versions, and can be deleted during the import process.
Also, Network switches will have another GUID, but the import allows you to change to a new switch
I hope you like that feature as much as I do.