NixOS is now almost usable as a desktop OS ;-). We have an X server, a bunch of Gnome packages, basic wireless support, and of course all the applications in Nixpkgs that we had all along running on other Linux distributions. Here are a few screenshots:

• X server with Compiz window manager.
• Emacs and a few terminals showing off the (near) absence of /lib, /bin etc.; everything is in the Nix store.
• Some applications.