users.rb
devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable, :omniauthable

#...field setups for devise...
  #
  ## Provide foundation to support multiple omniauth providers
  #
  embeds_many :authentications


  field :name,            :type => String
  field :provider,        :type => String  # TODO: This is a complete hack, better way?
  
  validates_uniqueness_of :email
  attr_accessible :name, :email, :password, :password_confirmation, :remember_me

  index( { email: 1},                         { background: true, unique: true } )
  index( { "authentications.provider" => 1 }, { background: true } )
  index( { "authentications.uid"      => 1 }, { background: true } )

  def self.new_with_session(params, session)
    #
    ## When omniauth is generating the user data this method is requested
    #
    if session["devise.user_attributes"]
      auth = session["devise.user_attributes"]
      new do |user|
        user.name    = auth['info']['name'] unless auth['info']['name'].blank?
        user.name  ||= auth['info']['nickname'] unless auth['info']['nickname'].blank?
        user.name  ||=auth['info']['first_name'] + ' ' + auth['info']['last_name'] unless auth['info']['first_name'].blank? || auth['info']['last_name'].blank?

        user.email   = auth['info']['email'] unless auth['info']['email'].blank?
        
        user.provider = auth['provider']
        
        #
        ## This password stuff is a complete hack
        #
        user.password, user.password_confirmation = auth['credentials']['token']

        user.valid?
      end
    else
      #
      ## We don't have a omniauth hash, so default to normal devise registration
      #
      super
    end
  end
  
  def password_required?
    super && provider.blank?
  end

  def update_with_password(params, *options)
    if encrypted_password.blank?
      update_attributes(params, *options)
    else
      super
    end
  end

Authentication.rb
class Authentication
  include Mongoid::Document

  field :provider,    :type => String, :default => ''
  field :uid,    	  :type => String, :default => ''

  embedded_in :user
  #
  ## TODO:  At the least, we'll want to add in data hooks for FB
  ## 	   for posting to user's wall, events, etc.
  #
end  

authentication_controller.rb
class AuthenticationController < Devise::OmniauthCallbacksController
	
  def all
    auth = request.env['omniauth.auth']
    authentication = User.first.authentications.where(:provider => auth['provider'], :uid => auth['uid']).first
      if current_user
	#
	## we've got a logged in user, lets see if they have already linked their account
	#
	if current_user.authentications.where(:provider => auth['provider'], :uid => auth['uid'])
	  flash.notice = "#{auth['provider']} is already linked to your account."
	  redirect_to '/'
	else
	  current_user.authentications.create!(:provider => auth['provider'], :uid => auth['uid'])
	  flash.notice = "Sucessfully linked your #{auth['provider']} to your account!"
	  sign_in_and_redirect current_user #TODO: think about redirection
	end

      elsif authentication
	#
	## We don't have a currently logged in user but we do have this provider and uid
	#
	flash.notice = "Signed in via your #{auth['provider']} account!"
	sign_in_and_redirect(:user, authentication.user)

      elsif user = create_new_omniauth_user(auth)
	user.authentications.create!(:provider => auth['provider'], :uid => auth['uid'])
	flash.notice = "Sucessfully created account!"
	sign_in_and_redirect user #TODO: think about redirection

      else
	session["devise.user_attributes"] = auth
	redirect_to new_user_registration_url
      end
    end
    
    alias_method :facebook, :all


#  def destroy
#  	@authentication = current_user.authentications.find(params[:id])
#  	@authentication.destroy
#  	flash.notice = "Successfully destroyed authenication!"
#  	redirect_to root
#  end

  def create_new_omniauth_user(auth)
    user = User.new_with_session(auth, session)
    if user.save
      user
    else
      nil
    end
  end
end

In routes.rb I changed the controllers: {omniauth_callbacks: "omnitauth_callback"} to
controllers: {omniauth_callbacks: "authentication"}