What does Drush error "Unknown option: --db-url" mean?
Pantheon site aliases are only compatible with Drush 5. I had the same message when trying to use Drush 6.

On a Mac with Homebrew, I ran "brew install drush5" and then symlinked the resulting file (/usr/local/Cellar/drush5/5.9/libexec/drush) to "/usr/local/bin/drush5" not to interfere with my existing Drush installation.

Now I can run commands such as "$ drush5 @pantheon.xxx uli" when needed for Pantheon.