Found a great post about active record tips and trick here:
One more thought about the use of concerned_with. I prefer to use require_dependency directly. So I don't need to add and load concerns.rb for every new Rails project and get more flexible to organize related files.
When you want to separate full text search config code to another file, remember to inherit the class from ActiveRecord::Base in order to let enable ThinkingSphinx plugin or UltraSphinx plugin methods.