This is totally subjective, so feel free to ignore this (yes, I can be anal), but I prefer formatting `private` declarations like so:

``` ruby
class Foo
  def some_public_method
  end

private

  def some_private_method
  end
end
```

This keeps all methods indented at the same level but also indents private methods under `private`, since, semantically, they are all affected by it.