Integrating an existing website with Facebook Connect using Facebooker is fairly easy. Several tutorial have been made; the best I found being:

• Mike Mangino’s one (Mike is one of the Facebooker authors)
  Mike also released the book Pragmatic Developing Facebook Platform Applications with Rails at the marvelous Pragmatic Booksheld.
• Integration with Restful_authentication by Made by Many
• french speaking people may prefer the one from PepperonRails

However, there is no description on how to handle a frequent use case where the user has been authentified in your application using Facebook Connect and disconnects in the Facebook website.

In this case, you will surely meet the famous:

Facebooker::Session::SessionExpired (Session key invalid or no longer valid)

When the exception occurs, you have to remove the facebook session informations AND facebooker cookies.
Indeed, the set_facebook_session will recreate the facebook_session with these cookies. If you do not remove them, you will loop again and again in your rescue_from handling.

Here is an example of what you can do:

class ApplicationController < ActionController::Base
...
  rescue_from Facebooker::Session::SessionExpired do |exception|
    clear_facebook_session_information
    clear_fb_cookies!
    reset_session # i.e. logout the user
    flash[:notice] = "You have been disconnected from Facebook."
    redirect_to root_url
  end
...
end

Dead simple, huh?