Ubuntu 11.04 Natty Narwhal does not come out of the box playing DVDs but with 2 simple commands you will be watching DVDs in a flash.
Open a Terminal Window Ctrl+Alt+T
sudo apt-get install ubuntu-restricted-extras
Insert DVD and enjoy.
I noticed during playback of my DVD that the picture was a bit wobbly. There is an easy fix for this.
Go to Edit>Preferences>Display Tab and check the box that reads disable deinterlacing of interlaced videos.
Next close down the Movie Player and reopen it and the wobbly screen should be gone.
Another option that is worth enabling is the play video where you left off.
Go to Edit>Preferences>General Tab and check on Start playing files from last position.