On the matter of productivity, the abstraction mechanisms offered by the Ruby language help to structure code and avoid repetition and that's certainly noticeable in comparison to Java (though, in my opinion, not in comparison to Scala, and probably also not in comparison to Smalltalk, ML, Haskell or Oz). That gain is offset to a point by the lack of refactoring tools. There are some who argue that those tools are made necessary by the verbosity of Java, and aren't needed in better languages. That's nonsense. If a language has an abstraction mechanism, that mechanism is used to define an abstraction and to use the defined abstraction elsewhere. If we then want to change the abstraction we must change code at the use sites as well, and that's where such tools can help. This is all so obvious that I find it almost silly to have to write it down.
Many of the abstraction gains in Ruby come from metaprogramming techniques. I'm not completely sold that they are necessary to achieve the level of abstraction attained, and I'm sure that they hinder readability. It's much easier to gain a footing in a library written with straighforward composition mechanisms (be it functions or classes and objects) than in a mess of Strings and calls to define_method and cousins.
While on the subject of abstraction, I have to comment on Rails. It's a mature web framework that does a masterful job of making the common cases easy. This is a much harder feat than it sounds, as we can glean from the failure of JSF, WebForms and similar unsuccessful attempts to abstract the web. The hidden cost of the bargain is when we get to the uncommon cases. It isn't so much the case that there are specific application features that are hard to code in Rails, though it happens, but that the structure of the code that Rails mandates sometimes isn't a good fit to the problem being solved.
I'm sounding a little negative, so let me balance it out by saying that I believe Ruby and Rails were as adequate choices for our project as any. The main reason is the availability of decent quality libraries and tools (refactoring and code navigation notwithstanding), specially in the often overlooked front of deployment and configuration management.
Apologies for an opinionated blog post.
1. Unittyped, for the pedantic.
2. Such as Agda or Coq, or some styles of programming in ML, Haskell or Scala.