gistfile1.rb

  # Current version
  # - before block runs before each example
  # - isolated examples
  describe "GET show" do
    before do
      @customer = create_customer
      get :show, id: @customer.id
    end

    it { should respond_with(:success) }
    it { should render_template(:show) }
    it { should assign_to(:customer).with(@customer) }
  end  

  # Proposal
  # - before block runs once - for customer controller spec
  #   time went from 8 to 3 seconds
  describe "GET show" do
    before do
      @customer = create_customer
      get :show, id: @customer.id
    end

    it "is successfull" do
      subject.should respond_with(:success)
      subject.should render_template(:show)
      subject.should assign_to(:customer).with(@customer)
    end
  end

  

I agree with @tfwright and @jmazzi