When I upgraded my Citrix Receiver 3.0 to 3.1, I ran into the fact that a https address instead of a http must be configured in the preferences.
There is a way to allow configuring http instead of https. This can be done by adding/changing the following registry keys:
HKLM\SOFTWARE\Citrix\AuthManager (on a 32-bit machine) or HKLM\SOFTWARE\Wow6432Node\Citrix\AuthManager
My highly appreciated colleague Nando pointed me to this article on XenAppBlog where it says:
“The newest Citrix Receiver for Windows 3.0 (220.127.116.1185) requires almost 150% more memory per user than Citrix ICA Client 11.2. So when optimizing you Citrix servers for the highest user density you should consider if you even need some