Step Three A: Configuring Xgl for GDM (Gnome users)
For Nvidia Ubuntu (Gnome) users, we start off editing /etc/gdm/gdm.conf-custom making the end look like this (some overlap provided for reference):
[servers]
0=Xgl

[server-Xgl]
name=Xgl server
command=/usr/bin/Xgl -fullscreen -ac -accel glx:pbuffer -accel xv:fbo
flexible=true