While this may be more obvious to some, I wanted to share the command that is needed with the latest WTOS (C10 and V10 tested) in order to map local USB drives in Citrix XenApp 5/6 application farms.
After much searching, I did the un-thinkable and opened the hotfix_README.txt contained with the downloaded and discovered the following text in the 'Additional Information' section:
If you are using Citrix XenApp and want to map USB disk drives, you will need to add "Sessionconfig=all unmapusb=yes mapdisks=yes" in your INI file. This disables HDX USB (which only XenDesktop supports) and allows the traditional disk drive mapping to be enabled. We know have Z$ back while using Citrix XenApp with the latest WTOS.
For our XenDesktop users, we adjusted their macAddress.ini file to disable the 'un-mapping':