RubyMine 4.0 also comes with new and improved support for other languages including CoffeeScript, HAML, SCSS and LESS. CoffeeScript sources can now be compiled to JavaScript directly in the IDE. And while release 3.0 focused on Rails 3 support, code coverage and improved debugging, RubyMine 4 provides performance enhancements, polishing and incremental improvements. See JetBrains full release here: http://www.jetbrains.com/ruby/whatsnew/?top40