detach/reattach remote GUI applications?

[Luke Dean]

I run a headless server and I've become fond of using the "screen" 
utility with SSH to allow me to launch a text-based application, detach 
from it, and then reattach to it later to see how it's going.

I'm wondering if there's a tool I can use that would allow me to do that 
with GUI applications.  I know that I can tunnel X over SSH to have my 
remote headless server do the processing and my local machine do the 
display, but sometimes I have to switch off my local machine.  This kills 
the display and thus kills the application.  I might be able to figure out 
a way to set up a logical display on the remote machine, but then I 
wouldn't know how to "see" it.  I'd have to tell the client application to 
switch Displays midstream wouldn't I?  Can that be done?

Windows Terminal Services (RDP) gives the capability I'm looking for by 
"disconnecting" and "reconnecting" a session.  Surely there's some way to 
get this capability with X, and I just don't know how.