OpenOffice is now in Nixpkgs (screenshot of OpenOffice 2.2.1 running under NixOS, and another screenshot). Despite being a rather gigantic package (it takes two hours to compile on an Intel Core 2 6700), OpenOffice had only two “impurities” (references to paths outside of the Nix store) in its build process that had to be resolved — a reference to /bin/bash and one to /usr/lib/libjpeg.so.
Armijn Hemel, Wouter den Breejen and Eelco Dolstra contributed to the Nix expression for OpenOffice.