While Chromium team ppas won't release new versions of Chromium browser, Alex Shkop will try to maintain more-or-less fresh releases of Chromium. Two PPAs were built for Chromium stable and Chromium development version. Install Latest Version of Chromium: For now, two PPAs only provide packages for Ubuntu 12.04.
To add Chromium Stable PPA (currently it's version 21):
sudo add-apt-repository ppa:a-v-shkop/chromium
To add Chromium Dev PPA (currently it's version 23):
sudo add-apt-repository ppa:a-v-shkop/chromium-dev
After added a PPA, update your repository and install Chromium:
sudo apt-get update
sudo apt-get install chromium-browser