I have been using Netbeans this year for most Java, Ruby, and Ruby on Rails development. Except for Ruby on Rails development, I think that I may switch back to Eclipse because of the Mylyn sub-project. I blogged about Mylyn a year and half ago (when it was called Mylar) and I recently gave the latest versions of Eclipse and Mylyn another try with Java, plain Ruby, and plain Python projects.
Mylyn treats tasks as first class objects that aggregate developer experience with specific source files, emails, web sites visited, bug tracking systems, etc. In the simplest use, you create tasks and let Eclipse know which task that you are working on. Mylyn remembers which files you edit, etc. and only shows you working material that you use most for the current task. You can easily switch back to a "show me everything" mode. Switching tasks immediately changes Eclipse to show you only the working materials for the newly selected task.
As a developer it feels very comfortable to see just what you need as you switch tasks. I like to turn off email and the telephone during development to reduce distractions. Having an IDE hide everything but the working material for the task at hand also helps to stay focused. Cool stuff!