Screenshot Grub boot menu showing the ability to boot into previous system configurations. Changing the system configuration is non-destructive: previous configurations are still there until you garbage-collect them.
Screenshot X server with Compiz window manager.
Screenshot Emacs and a few terminals showing off the (near) absence of /lib, /bin etc.; everything is in the Nix store.
Screenshot Some applications.
Screenshot KDE 4.2: switcher.
Screenshot KDE 4.2: exposé.
Screenshot Xfce desktop environment 4.6.2.
Screenshot KDE 3.5.
Screenshot Wine, Dosbox, Quake 3, plus a Mega Drive emulator.
Screenshot OpenOffice 3.0.1.
Screenshot OpenOffice 2.2.1.
Screenshot VirtualBox on NixOS running Vista and NixOS guests
Screenshot NixOps after having deployed a network of three VirtualBox machines