I gave a 5-minute lightning presentation at the October 2011 Drupal NYC meetup about Roger Lopéz's phpsh plugin for drush.

phpsh is a project by Facebook that provides a much more useful REPL (read-eval-print-loop) environment for PHP, similar to Ruby or Scala. The Drush phpsh plugin adds an easy way to generate ctags for code completion in your phpsh (as well as your favorite editor) and a way to run a persistent PHP session with a fully bootstrapped Drupal instance. It's really useful for testing out APIs.

If you missed it in person, you can watch the video embedded below.