Most experienced Ruby developers have come across the concept of metaclasses or singleton classes. Still this seems to be something obscure and rarely used, even though we all benefit from singleton classes every day. mehr
When models and controllers are supposed to be skinny, Rails clearly lacks a place to put all the extracted code. While there is a variety of different approaches, we like to keep it simple, stupid™.
There is a long going discussion on fat-this and skinny-that when building software systems. Obviously, you want to avoid fat classes all over, but where do you put the code then?