In ruby there isn't a lot of (any?) tool support for automated refactorings, the reason being that the ruby language is extremely dynamic and objects can be defined at runtime. It's pretty hard to detect something that doesn't exist yet :)
I believe RubyMine may have the closest thing to refactoring support, but I haven't ever used it so I wouldn't trust my judgement on that.
Most people I know just use textmate or vim with various plugins, macros, and bundles.
Thus, it is more important than ever to lock down existing behavior with characterization tests / integration tests.
Katrina is right in that a lot of the reason for the lack of IDEs with features comparable to those in the Java world is due to the dynamic nature of ruby. It's technically difficult to know what methods exist, for example, when methods are often created at runtime.
On the other hand, this same dynamic nature makes a lot of the refactorings that IDEs traditionally offer less important. Ruby enables very DRY code, meaning there's very little boilerplate sitting around, and most refactorings are just as easy to accomplish with a good text editor.