LibreOffice 4.0 Final is now available via the LibreOffice PPA. To install it in Ubuntu 12.04 or 12.10, follow the instructions below:
sudo add-apt-repository ppa:libreoffice/ppa
sudo apt-get update
sudo apt-get install libreoffice
LibreOffice 4.0 Beta 2 is currently available by default in Ubuntu 13.04 Daily Build.
Features of 4.0 Final
It has an impressive list of new features:
now integrates with various CMS (Content Management System)
uses Firefox personas to theme it
contributing to LibreOffice is easy using Gerrit
converting non-native formats is now improved
can edit Visio and Publisher documents
How to Install Personas
Open up LibreOffice and go to Tools-Options-Personalization. Click the Select Persona button, and in the Persona address field, enter the link to the desired Firefox Persona (e.g. this example uses http://www.getpersonas.com/en-US/persona/462094.