Yep, several apps aren't available in ICS that were in GB. Have you tried uninstalling and reinstalling the app?
Let's find your missing app enviroellen! With the update, the app icon looks a little different (it's at the bottom looks like a little circle with 6 dots). Please select it and make sure at the top left corner it says "all apps". If not, please click on the little icon next to what is written in the top left corner and once it says "all apps" scroll through the pages and see if you can find the Citrix Receiver app and if you see it then touch and hold it until it moves to the home screen.
If you weren't able to find the app, go to Settings>Applications>Manage Applications>tap on All and see if you can find the Citrix Receiver app. If you find the app, select it and chose Clear Cache and then reboot your phone.
Keep us posted if you continue to have trouble finding your important application.
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Yes, when I uninstalled the app and reinstalled it, the app reappeared on both the home screen and the app lists. For the record, It now shows up as "Receiver", rather than as "Citrix Receiver".
(I didn't try uninstalling the old copy of app until I was at my workplace during the business day, so I could get help with the installation settings in case something didn't get set up properly.)