RoR inherently supports a restful architecture, so you’re already at an advantage there.
RoR also supports a very clean MVC paradigm So it’s easy to implement a layered web-application. Parials allow you to define a shared structure in the views to remain DRY.
Controllers allow you a clean way to orchestrate behavior and redirection.
Models along with ActiveRecord support eases your integration with the DB.
The most useful aspect to Rails is how based on naming convention, elements of the db, model, controller and views are tied together.

In general, I have seen some implementations where the controller (along with the helper framework) can become a bit heavy-weight, however, you can design your system to be bottom (as in model) heavy, and have the business logic + CRUD pushed in the models. By doing this, you could lose a bit of the Rails ‘magic’, but it’s still a good strategy if you want to expose the model through web-services (Rails has support for this as well) that are not RESTful (WSDL or XML-RPC based)

Are you guys using a RESTful architecture style? Any insight you can provide into how you decided on how to design layered application?