RBrainz now has an Ubuntu package repository on launchpad. This makes it really easy for Ubuntu users to install RBrainz and MB-DiscID and to stay up-to-date when new versions get released. You can browse the repository on https://launchpad.net/~phw/+archive.

To use the repository add the following line to your sources.list:

deb http://ppa.launchpad.net/phw/ubuntu gutsy main