I have the same issue as http://stackoverflow.com/questions/3027555/creating-an-additional-related-model-with-devise (which has no answer).
I have overridden the devise view for creating a new user and added a company name, I have changed the model to use accepts_nested_attributes_for
There are no errors, but it is not adding the nested record and I don't have a controller where I can modify the request.
I have the following (shortened to make it readable):
routes.rb
map.devise_for :users
map.resources :users, :has_many => :companies
user.rb
has_many :companies
accepts_nested_attributes_for :companies
devise :registerable ... etc
company.rb
belongs_to :user
new.html.erb
...
<% form_for resource_name, resource, :url => registration_path(resource_name) do |f| %>
...
<% f.fields_for :company do |company_form| %>
<p><%= company_form.label :name %></p>
<p><%= company_form.text_field :name %></p>
<% end %>
...
UPDATE: I didn't add :company to the attr_accessible list in the User model.