The possibilities of GTK theming are very interesting, but the result is ugly, it doesn’t fit. See:

http://f.cl.ly/items/3S033x090a370x1u0S3h/osx-ubuntu.png

http://f.cl.ly/items/0Y1H0X0l45272l2j401t/osx-ubuntu-2.png

http://f.cl.ly/items/1a3o1x2a0g0v161v062j/osx-ubuntu-3.png