Tor Norbye is a programming machine on par with the legendary Ola of Bini. He's the one-man force working on NetBeans Ruby support, and his progress has been epic. Here's his latest screenshot and a short blurb about it:

NetBeans + Ruby = True

In just over two months' time, Tor seems to be (in my opinion) on the verge of eclipsing every other Ruby editor/IDE out there. I've been using development builds of his stuff and it's really superb. A few features I've missed before that are now rapidly maturing in NB+RB:

• Highlight usages: not genius, but smarter than dumb-as-a-post right now; great for local and block vars, getting smarter for methods
• Clickable methods and variables: limited to method-scope for variables or file-scope for methods, but coming along very quickly...and even those limited scopes are way better than nothing at all. I don't know how many times I've wanted to Ctrl-Click a method in some giant Ruby file and go straight to the method def. Awe-some.
• Inline refactoring: I've demoed this a couple times, but for local and block vars you can do inline renaming...essentially renaming all instances of the variable at the same time. It's really nice, looks cool, and represents the tip of the iceberg for refactoring capabilities.

There's plenty of other stuff that's cool, like the Navigator view of a file (shows classes, modules, methods, of currently-selected file), AST view (great for us Ruby language hackers that like to see the actual structure of things), and more.

Things are definitely shaping up nice for next-generation Ruby IDEs.