Note: this has been verified to work on 11.04 (Natty), 11.10 (Oneiric) & 12.04 (Precise)

To convert a DVD and make it viewable on your mobile device Handbrake seems to be the most useful tool I have discovered so far. Since it is not part of the default Ubuntu Repositories here is the installation process. The first step is to insure libdvdcss2 is installed

sudo apt-get install libdvdcss2
sudo add-apt-repository ppa:stebbins/handbrake-releases
sudo apt-get update
sudo apt-get install handbrake-gtk