What do you want to know about OOP and Rails?

For a long time I’ve had the idea in my head of doing a Rails app-building walkthrough that emphasizes classic Object Oriented Programming techniques. For instance, building out domain models as regular ole’ objects, and then adding persistence in as an implementation detail later on.

Over the weekend I started writing it. I thought it was just going to be a sort of maxi-article, but I’m at 37 pages and I’m only 2/3 done at best. So far I’ve covered stuff like adding ActiveModel bits as-needed, Dependency Injection, and the Presenter pattern, but I’m sure there’s stuff I’ve missed. So I thought that while I’m in the process of brain-dumping all of this stuff I might as well open up the floor.

SO! What would you like to know about OOP on Rails?