Rails i18n and yml structure for form labels

According to the ActionView documentation. Quote:

The text of label will default to the attribute name unless a translation is found in the current I18n locale (through views.labels.<modelname>.<attribute>) or you specify it explicitly.

I have a "user" model and a registration form. Here's a snippet of the relevant part:

<% form_for(@user) do |f| %>
    ...
    <p>
    <%= f.label :username %>
    <%= f.text_field :username, :class => 'full_width' %>
    </p>
    ...
<% end %>

Dots hide unimportant code.

As I understand the documentation, if I provide a translation in my locale file, in this case :dk, my dk.yml looking like so:

dk:
    views:
        labels:
            user:
                username:
                    "blahblah"

Rails should translate the label text and insert "blahblah" instead of "Username".

This is not happening, so I must have missed something. Any help appreciated.