Here's how you can get rid of the ugly white dots on the Ubuntu 13.04 login screen.
1. Open a terminal window.
2. Type in the following commands then hit Enter after each.
sudo xhost +SI:localuser:lightdm
sudo su lightdm -s /bin/bash gsettings set com.canonical.unity-greeter draw-grid false
For more, see the original article at the link below.