Most IDEs present the project structure in a top down manner. This is great way to explore at a high level when joining an existing project. However, after working on the same project for more than a year, I realized that this approach can become counter-productive.
After Oracle declared the end of Ruby in NetBeans, I switched to Vim. By using a command line and an editor as the only tools, I was forced to mentally switch to a bottom-up perspective. To my amazement, I discovered that this made me more focused and productive. As a bonus, I got first class HAML and SASS syntax support.
I recommend Vim + Rails plugin for anyone that will work on a single project for an extended period of time.