Dualbooting the Samsung Series-5 (I have the 3G version) with Ubuntu is actually a lot easier than expected and is almost the same as dualbooting on the CR-48 (Google’s beta program to Chromebooks). Online there aren't many tutorials on how to do this because the method used on the CR48 still works perfectly. You can find the tutorial HERE, and I personally only had one problem throughout the whole process.
After Ubuntu is installed for some reason my Chromebook wouldn't boot into my Linux partition. After trying all of the possible commands, I decided I needed to do some more research, and discovered my boot-up screen looked different from other people’s. They had a massive blue frowning computer picture when booting while I only saw some ASCII art. It turns out, once you boot into developer mode, you need to install a developer BIOS. To do so you open the terminal (Ctr Alt ->) and type in the following.
localhost login: chronos
chronos@localhost $ sudo bash
localhost chronos # chromeos-firmwareupdate --mode=todev
|When you restart, your computer startup screen should look like this (press Ctrl+D to skip)
After running that, you will want to re-run the startup script ‘wget http://goo.gl/hnkxo; sudo sh hnkxo’. Your Chromebook should now boot up into Ubuntu! If you want to easily switch between them click HERE for a simple tutorial. If you have any issues feel free to comment here, or tweet me @RoboTechEd.