That was suspiciously easy - I now have LibreOffice in place of OpenOffice on Mint 9.

Be interesting to see how it works. It seems to open documents impressively fast, but I've not tried beyond that.

If anyone wants to switch from OpenOffice to LibreOffice on an older Mint (and presumably other Ubuntu-based) distro, many thanks to the chap who wrote the tutorial I used:

http://community.linuxmint.com/tutorial/view/336

Just involved the following commands in a terminal, and went very quickly:

sudo apt-get purge openoffice*.*

sudo add-apt-repository ppa:libreoffice/ppa

sudo apt-get update

sudo apt-get install libreoffice

sudo apt-get install libreoffice-gnome

(or  sudo apt-get install libreoffice-kde  if appropriate)

sudo apt-get install language-support-en

Done!