Edit: Due to the fact that this article is old, the installation instructions may not work anymore. In order to successfully install the latest version of LibreOffice, please access the libreoffice tag and open the latest article (the one on top).
Now, LibreOffice 4.2.1 RC1 has been developed, being available for Ubuntu 14.04 Trusty Tahr, via the LibreOffice PPA. For information about LibreOffice 4.2.1 RC1, see the official release notes.
In this article I will show you how to install LibreOffice 4.2.1 RC1 on Ubuntu 14.04 Trusty Tahr.
So, all you have to do is add the needed ppas to your system, update the local repository index and install the libreoffice package. Like this:
$ sudo apt-get purge libreoffice-core
$ sudo add-apt-repository ppa:libreoffice/libreoffice-prereleases
$ sudo apt-get update
$ sudo apt-get install libreoffice