Here's a slightly cleaned-up version that also supports Webkit. DISCLAIMER: It's based on the code above so it's supposed to work with Selenium & RackTest *but* I've only tested it against Webkit. It does not support the @announce tag.

gistfile1.txt

module CookieStepHelper
  
  class Cookies
    def Cookies.for(session)
      case session.driver
      when Capybara::Driver::Selenium
        SeleniumCookies.new(session.driver)
      when Capybara::Driver::RackTest
        RackTestCookies.new(session.driver)
      when Capybara::Webkit::Driver
        WebkitCookies.new(session.driver)
      else
        raise "Unsupported driver."
      end
    end
    
    def all_cookies
    end
    
    def delete_cookie(cookie_name)
    end
    
    def to_s
      all_cookies.map(&:inspect).join("\n")
    end
  end
  
  class SeleniumCookies < Cookies
    def initialize(driver)
      @browser = driver.browser
    end
    
    def all_cookies
      @browser.manage.all_cookies
    end
    
    def delete_cookie(cookie_name)
      @browser.manage.delete_cookie(cookie_name)
    end
  end
  
  class RackTestCookies < Cookies
    def initialize(driver)
      @driver = driver
    end
    
    def all_cookies
      cookie_jar.instance_variable_get(:@cookies)
    end

    def delete_cookie(cookie_name)
      all_cookies.reject! do |existing_cookie|
        existing_cookie.name.downcase == cookie_name
      end
    end
    
    private
    
    def cookie_jar
      @driver.current_session.instance_variable_get(:@rack_mock_session).cookie_jar
    end
  end
  
  class WebkitCookies < Cookies
    def initialize(driver)
      @browser = driver.browser
    end
    
    def all_cookies
      @browser.get_cookies
    end
    
    def delete_cookie(cookie_name)
      cookies = @browser.get_cookies.reject {|cookie| cookie[/#{cookie_name}=/]}
      @browser.clear_cookies
      cookies.each {|cookie| browser.set_cookie(cookie)}
    end
  end
end

Then /^show me the cookies!$/ do
  cookies = CookieStepHelper::Cookies.for(Capybara.current_session).to_s
  puts "Cookies: #{cookies}"
end
 
Given /^([a-zA-Z]+) closes (?:his|her) browser$/ do |user|
  Capybara.session_name = user
  session_name = .... # Provide session name, read it from Rails config etc.
  CookieStepHelper::Cookies.for(Capybara.current_session).delete_cookie(session_name)  # Criticue-specific.
end