Enabling Remote X11 Forwarding Over SSH Despite IPv6 Bug

Run ps -ef | grep X on your X client (the remote box) and your X server (in this case, you local machine in which you intend to have the GUI application displayed)

Your output SHOULD look very similar to this:
/usr/bin/X :0 vt07 -nolisten tcp

It is perfectly acceptable that the -nolisten tcp is enabled and running on both the X client and X server

/etc/ssh/ssh_config (Your local machine i.e. your ssh client)

Host *

ForwardAgent no

ForwardX11 yes

ForwardX11Trusted no

/etc/ssh/sshd_config (Your sshd server i.e. your remote ssh server)

X11Forwarding yes

X11DisplayOffset 10

Try running xclock.  At this point, I was getting:

Error: Can't find display

And running:

echo $DISPLAY

resulted in nothing.

If you experience similar issues, you've configured the options in /etc/ssh/ssh_config & /etc/ssh/sshd_config, and get the following error when authenticating with your ssh server (evident on sshd server by running tail -f /var/log/auth.log):

error: Failed to allocate internet-domain X11 display socket.

Then ensure the following is configured within /etc/ssh/sshd_config:

AddressFamily inet

Restart your sshd server:

/etc/init.d/sshd restart

Exit your shell by hitting CTRL+d

Re-authenticate:

ssh -X <user>@<host>

echo $DISPLAY

and you should see:

localhost:10.0

Run xlock and viola!  Awesomeness.  Cheers!