The Beefy Miracle wallpaper is not very pleasing to the eye so I looked into changing GDM background on Fedora 17 Linux. In order to accomplish this feat, we can use gdm3setup.
To get gdm3setup, clone its git repository:
git clone https://github.com/Nano77/gdm3setup.git
Then run install.sh script as root to install. It will install a shortcut (.desktop file) so the application is accessible from the Applications list as GDM3 Settings.
Apart from changing the wallpaper, it offers a few more options for customization of both GDM and Gnome Shell, like cursor theme, GTK theme, logo, etc.