A week or so ago, the Ruby Draft specification made the rounds
Yes... Ruby is finally getting a standard. While RubySpec has been around for a while, and is a great, it is an executable specification that tells you what, not why, and it aims to be "complete" while the new project aims to define a shared core suitable for implementation by all the different Ruby implementations that are springing up.
I think they're complementary enough that the Ruby Draft Specification could be very beneficial.
For my compiler project this means there's now a compelling reason to revisit some things (such as the parser) to look at conformance, and a clear roadmap for some others (classes) to ensure it at least meets the spec.
Of course, in many ways MRI will still be the benchmark, but the standard will provide a minimal level of conformance that will likely be easier to achieve.
In particular, the spec includes a formal grammar for Ruby that doesn't involve walking through thousands of lines of code written for another implementation to verify that you're doing things right. I'm particularly looking forward to going through my parser and aligning it more closely with the draft spec... (I'm sure I'll be swearing a lot while doing it, though)
It also includes descriptions of expected semantics for things like the object model that have previously been something a lot of people (including me) have spent time revers engineering to figure out.
Combined with all the Ruby implementations in progress, this is a clear indication that Ruby is growing up and becoming a contender in areas where it would previously not be acceptable.
Keep an eye on the Ruby standard project...