Yesterday Tom Enebo announced the availability of the community Ruby plugin for NetBeans IDE 7.1.
Installs without a hitch. Seems to work as one would expect. Here you see the Projects window showing a structured view of a Ruby sample project, together with the Ruby editor:
As always, start your development work by going to File | New Project and then select one of the Ruby or Ruby on Rails templates that have been registered there by the plugin.