Sorta Updated: Samsung XE303C12 ChrUbuntu Boot from SD or USB

Note:

USB3.0 slot will not work as a boot device. 
USB2.0 slot will work as a boot device. 
SD slot will work as a boot device.

Switch to Dev Mode: ESC + refresh + Power
1. Connect to WiFi
2. Agree to Terms
3. Drop to Shell: At Logon Screen, Ctrl + => 
          (it's the key left of refresh key)         
4. Logon: username chronos
5. type: sudo chromeos-firmwareUpdate --mode=todev
6. Insert SD card and/or USB Device: type: lsblk
7. Take note of device name for your SD or USB device
       (usually either mmcblk1 or sda or sdb)        
8. Download: type: wget http://goo.gl/s9ryd
9. Execute install: type: sudo bash s9ryd ubuntu-desktop lts /dev/sda
10. Config Console Setup:  [UTF-8] [Combined - Latin; Slavic Cyrillic; Greek]
11. Plug in! Go get coffee! Walk dog! could be 3o min or so... just be patient...
12. Reboot > Dev Mode screen:
                     ChromeOS: Ctrl + D (default boot)
                     UbuntuOS: Ctrl + U (sd/usb boot)