VDA Not Saving Changes
I ran into an issue where a XenDesktop VDA didn't appear to be saving changes. This is a huge deal if the machine begins a Windows Update and the update requires a reboot. Yep, you've guessed it, it causes a continuous Windows boot loop. That's another issue in-and-of-itself. Check out that resolution here.
In earlier versions of the Citrix XenDesktop VDA software, there was a bug with the PVS agent software. Not really sure why they tried to bake that in, but I'm thinking it has to do with the way Citrix is trying to build MCS by borrowing some of the PVS methodology.
Anyway, the fix is to create the follow registry key:
Key Location: HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Session Manager
Data: PvsVmBoot (Add to last line)
Of course they blame it on 3rd party Antivirus, but given that it's fixed in later VDA versions, I find it a little odd.