I came across How do I install wallpapers from older releases?, and I was wondering if I could somehow get a GTK+3 version of the old Human theme used prior to 10.04 LTS to complete the retro look on 11.10 and later.
GTK+3 was not yet released at the time of the Human theme, so short answer is now. However, it shouldn't be terribly difficult for someone of sufficient skill, to take that theme, and port it to work with GTK+3 as well. Someone may have done so already, but searching on the various theme sites is left as an exercise for the reader. :)