In my rails 3 app I use Omniauth for the user authentication part (fb/twitter).
Actually I follow this:
https://github.com/RailsApps/rails3-mongoid-omniauth
Devise offers this functionality through its Rememberable module. OmniAuth integrates easily with it through the (you'd never guess it) OmniAuth module. It's even mentioned in the second link you posted!