One reason why I get the latest netbeans is ruby support. Netbeans it self have a ruby version, jruby, but it support the native ruby installed.
The difference between the both is, if you download the full version of netbeans, you will get jruby, without needing to install ruby on your system. Which features gems, too. On the other hand, native ruby is supported as well, it just that, netbeans do not have the necessary permissions, to access gems. But syntax, highlighting, works quite well.
So using it is a matter of selecting ruby on rails project under ruby, when you start a new project
And also a generator, to generate stuff, like model, scaffold, controller, and other thing that you done, on the rails generate script
But really, it is not much, it is just a gui for process that is usually done, on shell, nothing ground breaking here, just that having a ide that do syntax highlighting on ruby is quite cool.
p.s able to run ruby on netbeans without ruby, rocks too