This documents the Ctrl-F2 key Super(Window)-S key to break out of a Windows machine under Citrix and access other Linux Workspaces.
I access a Windows7 virtual PC through Citrix running on my Ubuntu12.04 Linux Desktop. The Host configuration causes Windows7 to run in full screen mode on one of the Ubuntu Desktops. The simplest way I found to escape from Citrix/Windows7 control to access Ubuntu workspaces is to first press left Ctrl/F2 together. Then press the Superkey (Windows logo)/s together. The Workspace switcher pops up like this:
Windows7 runs in the upper right workspace.
From here I am free to roam any work space, start other applications, close windows, and so forth by double clicking the appropriate window. Returning to Windows7 is a simple as accessing the Workspace switcher again and double clicking on the upper right workspace. I hope this simple trick is useful to you. Cheers.
I categorize this as travel also because having a virtual Citrix PC at work allows me to connect to work and keep on top of situations while travelling. I have connected not only sitting in a hotel room but on a bus between Riga and Vilnius.