Jakub Steiner proposed to use a darkish theme as the GNOME default. This is a really intersting idea and from a QA point of view it sound pretty sensible. The major problem with GTK is, that only known widgets are styled by themes. So hacky custom widgets are not easily themeable. Aside from that I have some concerns, wheither a dark theme would be associated with hacker desktop, the exact opposite of GNOME’s target.
Nevertheless I will try Darkilouche and gm-looks for a while now. I always disliked dark themes, don’t know exactly why but it is time to try again.