Running script/console provides the delightful answer:
/usr/local/lib/ruby/1.8/irb/completion.rb:10:in `require’: no such file to load – readline (LoadError)
Turns out that Kubuntu doesn’t have the curses libraries.
Here’s the begining of a solution
apt-get install libncurses5-dev libreadline5-dev (Ubuntu/Debian)
Then recompile the readline extension and go from there.
cd ext/readline ruby extconf.rb make sudo make install