Snapshots taking up tons of space on VM host machines

I found myself in a situation where I had a 1 TB drive on a VM host (running Windows 2008 R2) with four virtual machines on it that was completely out of space.  I found that there were tons of AVHD files taking up a lot of room.  Per what I read, these are snapshot files, even though I deleted the snap shots from the Hyper-V Manager (and cleared up a dozen GB or so), the snapshots were not truly gone.

This page talks a little bit about the process:

http://blogs.msdn.com/b/charles_sterling/archive/2008/08/06/what-are-all-these-avhd-files-hyper-v.aspx?Redirected=true

But in the end, I got the space back by just turning off the virtual machines.  When I did so, there was a merge process that went on with the snapshots.  In a turned off machine, this just happens automatically.  In the end, I turned off the machines and left them off until the "cancel merge in progress" went away.  For my largest VM (approx 400 GB of storage), this took about 4 hours.

This is what the cancel merge in progress looks like: