I would like to try out LibreOffice, but I'm worried about messing up my existing OpenOffice.org install. Can LibreOffice be safely installed alongside OpenOffice.org?
Yes absolutely. Considering you are using ubuntu and openoffice.org is installed by default, the libreoffice installer will install under the /opt directory thus not interfering with Oo installation.
Yes, it will be fine. it installs totally separate from OO
Yes, even though LibreOffice is a fork of OpenOffice it is a completely standalone application and will install (and uninstall) without changing anything to do with Openoffice.