I recently reinstalled my OS X 10.8 and I discovered that X11 (XQuartz) does not work anymore.
I do have XQuartz installed and started and I do see the DISPLAY variable being correctly set on terminal.
Still, when I do ssh to other machines, I do not see any DISPLAY variable set, so trying to start a X11 app will fail.
I can only assume that I'm missing something in my ~/.ssh/config but what? I already have:
ForwardAgent yes
ForwardX11 yes
Update! It seems I found the cause
ControlMaster auto
ControlPersist 3600
ControlPath ~/.ssh/master-%r@%h:%p
Still, I don't know why this breaks the DISPLAY part, as I did not had any existing connection already opened and I do want to take the benefit of reusing existing connections.