javascript.rb

# This works with steak 0.3.x and rspec 1.x
# For steak --pre and rspec 2 see this fork: http://gist.github.com/448487 

# Put this code in acceptance_helper.rb or better in a new file spec/acceptance/support/javascript.rb

Spec::Runner.configure do |config|

  config.before(:each) do
    Capybara.current_driver = :selenium if options[:js]
  end

  config.after(:each) do
    Capybara.use_default_driver if options[:js]
  end

end

your_feature_with_js_spec.rb

#...

scenario "Scenario that needs Javascript", :js => true do
  #...
end

scenario "Scenario that doesn't need Javascript" do
  #...
end

Thanks :)

Looks like that isn't required anymore: http://jeffkreeftmeijer.com/2011/capybara-ate-swinger/