Update to work with chosen jquery plugin. If don't know the id of the select and find option by text rather than id. Whitout using execute_script

jquery_chosen_helper.rb

# Example:
#  chosen_select 'select[name="projects"]', "ProjectA"
#

def chosen_select (css_select, option_text)
  element_id = page.find(css_select)['id']
  page.driver.browser.mouse.down find("##{element_id}_chzn").native
  within("##{element_id}_chzn") do
    find(:xpath,"//li[text()=\"#{option_text}\"]").click
  end
end

For current version of capybara and choosen this working:

  def chosen_select(css_selector, value)
    page.evaluate_script(%{$('#{css_selector}').val('#{value}').trigger("chosen:updated");})
  end