HT – http://martin.leyrer.priv.at/y2013/m03/Connecting_to_a_Raspberry_Pi_via_USB_TTL-Serial_with_Ubuntu_Linux.html

ls -l /dev/ttyUSB0 #verify device is attached
sudo adduser [the user you want to add] dialout

REBOOT

sudo reboot now

CONNECT VIA TTL SESSION

screen /dev/ttyUSB0 115200

From Linux (Ubuntu) you can remote forward the x-windows GUI apps

ssh -YC user@ip

then run a gui app, ie: lxpanel, lxsession, wpa_gui