I know that you can drag files from one device to another with iTunes 11 and Homesharing. Does dragging achieve what you need? I found the new menu system to be a little complicated for this, so sometimes I turn on the side bar using View > Show Sidebar and that makes it a lot easier (for me at least) to add back and forth.
For the import button to show up then you need to ensure that the HomeSharing on eeach computer was set up with the same Apple ID. This may be different to what that machine uses to login to itunes. That does not matter.
If there are two different Apple IDs involved then you will have to authorise each machine with the other Apple ID
Store > Autorise this computer
Suggest you turn off Home Sharing
File > Home Sharing > Turn off Home Sharing on both machines.
Recreate the Home Share using the SAME Apple ID
This worked - it's the same steps used in the prior releases but for some reason I had to redo the steps after upgrading from 10 to 11.
What I was literally asking was "where is the button located?" - with the new (terrible) Show View I thought they had moved it. It still shows up in the same place, in an added bar at the bottom when you are eligible.