This demonstrates the passing case well, but to me the really interesting/useful part of this new feature is the failure case, for when you try to stub a method that doesn't exist.  It would be good to include at least one example demonstrating that when your stubbing or mocking doesn't match the interface, it fails with a useful error.   A suggested approach:

* Move the spec definition into the background section so we can re-use it.
* Add a scenario like so:

``` gherkin
When I rename the `ConsoleNotifier.notify` method to `ConsoleNotifier.send_notification`
  And I run `rspec spec/user_spec.rb`
 Then the output should contain "1 example, 1 failed"
  And the output should contain <some representative snippet of the not implemented failure message>
```

* Add another scenario like so:

``` gherkin
When I update the `ConsoleNotifier.notify` method to require a second `color` argument
  And I run `rspec spec/user_spec.rb`
 Then the output should contain "1 example, 1 failed"
  And the output should contain <some representative snippet of the arity failure message>
```

Thoughts?