It is also still much slower than Groovy and Scala, being at the same time similarly or even less expressive and having worse tooling. Therefore I can't see any reason to move from e.g. Java to Ruby. When Java is not expressive enough I'd consider using Groovy/Scala/Clojure.
Benchmarks these days show Ruby 1.9/2.0 as being a wee bit faster than Python, and it's improving. That's still much slower than Java, of course, but then that's a bad comparison; Ruby and Python are better comparisons.