Install Smoothly + Dark theme on Ubuntu 12.10/12.04/11.10/Linux Mint (GTK theme)

Install Smoothly + Dark theme on Ubuntu 12.10 Quantal/Ubuntu 12.04 Precise/Ubuntu 11.10 Oneiric/Linux Mint 13/12 (GTK theme)

Smoothly theme is available in two versions smoothly-dark and smoothly plain, It is available for GTK 3.6/3.4/3.2 versions.
Install Acyl Icons or Check Icons Collection
You can use these Tools to change theme and icons: Gnome Tweak Tool, Ubuntu Tweak

Theme tested on Ubuntu 12.10 Quantal Quetzal.

To install Smoothly theme on Ubuntu/Linux Mint open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal:

Terminal Commands:
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install smoothly-theme

That's it

Source: Smoothly