With classic Gnome, if one had two monitors, one could set up "separate X sessions" for each monitor. In this configuration, each monitor had a separate user login session and application windows were captive to the X session they were launched from. Is something similar possible with Gnome 3? If so, how do you go about setting it up?
This has nothing to do with the desktop environment you are going to use an this answer remains valid.
Basically you need to gather the names Xorg uses/gives your devices and monitors, then you combine devices and monitors to "seats". In
xorg.conf terminology seats are "ServerLayout" sections. Then you reconfigure your display manager to start multiple instances, each using a different ServerLayout.
The ServerLayout sections will look something like this:
Section "ServerLayout" Identifier "seatX" Screen X "ScreenX" 0 0 InputDevice "MouseX" "CorePointer" InputDevice "KeyboardX" "CoreKeyboard" EndSection Section "ServerLayout" Identifier "seatY" Screen Y "ScreenY" 0 0 InputDevice "MouseY" "CorePointer" InputDevice "KeyboardY" "CoreKeyboard" EndSection
and to reconfigure gdm, its configuration file will look something like this
[servers] 0=Standard0 1=Standard1 ... [server-Standard0] name=Standard server command=/usr/X11R6/bin/X -novtswitch -sharevts -layout seatX [server-Standard1] name=Standard server command=/usr/X11R6/bin/X -novtswitch -sharevts -layout seatY
[note]: shamelessly copied from the Gentoo Wiki