javascript.rb

# Adapted for Rspec2. This won't work in RSpec 1.
# Put this code in acceptance_helper.rb or better in a new file spec/acceptance/support/javascript.rb

Rspec.configure do |config|

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

  config.after(:each) do
    Capybara.use_default_driver if example.metadata[: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

example.options also works under RSpec 2.

Nice tip! Thanks wincent! :D

FYI: now you can do it just like this http://jeffkreeftmeijer.com/2011/capybara-ate-swinger/