Automated Testing Clinic follow-up: capybara-webkit vs. poltergeist/PhantomJS | Behind the Fan Door
http://behindthefandoor.fandor.com/2014/03/02/automated-testing-clinic-follow-up-capybara-webkit-vs-poltergeist-phantomjs/
poltergeist provides a handy method, page.driver.network_traffic, that one can call to see the network requests that were made as a page loaded.