Installing LibreOffice on your Ubuntu just became easier as there is a PPA available for it now. So there is no need to follow alternative methods we mentioned earlier.
LibreOffice packages ( version 3.3.0 RC) are available for Lucid, Maverick and Natty. Run following commands to install LibreOffice:
sudo add-apt-repository ppa:libreoffice/ppa
sudo apt-get update
Now for Ubuntu run following command:
sudo apt-get install libreoffice libreoffice-gnome
sudo apt-get install libreoffice libreoffice-kde