A couple of things that have stumped me today.
A syntax error in database.yml caused the TextMate model generator to die silently. In case of doubt, check the config.
After installing rFacebook on Dreamhost, the application would not pick up the gem without unpacking it and requiring the explicit path in production.rb:
require "#{RAILS_ROOT}/vendor/rfacebook-0.6.2/
lib/facebook_rails_controller_extensions"