Ubuntu includes Gnuradio Companion (GRC) 3.2.2 since Ubuntu 10.04. The included version has a small bug with the GRC crashing when trying to load its preferences, which makes it unusable (the error message is KeyError: ‘options’). A bug report has been opened; in the meantime, a workaround can be used:

touch ~/.gnuradio/config.conf
cat /etc/gnuradio/conf.d/grc.conf >> ~/.gnuradio/config.conf