If you prefer to make Ubuntu 12.10 (Quantal Quetzal) look like OS X Mountain Lion, I suggest that you try the Mountain-Lion GTK 3.6 theme, Mac OS X icons are also provided. The theme is compatible with Unity and Gnome Shell and can be easily installed in Ubuntu via our PPA. Here are two screenshots of Mountain-Lion theme under Unity:

Mountain-Lion Theme Installation

Under Ubuntu 12.10, open the terminal and enter these commands:

sudo add-apt-repository ppa:upubuntu-com/gtk+3.6 
sudo apt-get update 
sudo apt-get install mountain-lion-theme

Use now Gnome Tweak Tool to enable this theme.

Mac OS X Icons Installation

Via the terminal, issue these commands:

sudo add-apt-repository ppa:upubuntu-com/icons2 
sudo apt-get update 
sudo apt-get install ilinux-icons

Enable the set of icons with this command:

gsettings set org.gnome.desktop.interface icon-theme 'iLinux-icons'