With Ubuntu 14.04 Handbrake is now available straight from Ubuntu Software Center. So installing this useful tool is a simple search and click away.
The downside to the version supplied in Software Center is the lack of mp4 format support though. Those who need mp4 support in Handbrake will need to install from the snapshots PPA.
You can install it easily with a few simple commands:
~$ sudo add-apt-repository ppa:stebbins/handbrake-snapshots
~$ sudo apt-get update
~$ sudo apt-get install handbrake-gtk
That should do the trick.
Mp4 is not a open format so that unfortunately means it can't be easily included in the repository by default.