Sometime back I added the final ruby 1.9.2 build for Ubuntu Lucid. I have recompiled the same for Maverick today and have uploaded it to the ppa. Along with the ruby1.9.2 packages I have uploaded the ruby-default package too. This setups the update-alternatives system for different ruby versions. Read more about it here.
You can add the repository to your system using the following command.
sudo add-apt-repository ppa:pratikmsinha/ruby192+bindings
Once that’s done, update the apt cache and install the applications
sudo aptitude update sudo aptitude install ruby-full ruby1.9.2-full sudo aptitude install ruby ruby1.9.2 (In case you don't need the full ruby package)
You can now easy switch between different ruby versions using the update-alternatives system.
@~$ update-alternatives --list ruby /usr/bin/ruby1.8 /usr/bin/ruby1.9.2
If you want further guidance regarding adding PPA repositories look at this link. It has screenshots and alternate instructions for older ubuntu systems.