If it has not been rewritten using modern (good) Ruby style I guess it's still turning a perfect cartwheel. While reading Eloquent Ruby (by Russ Olsen) Ruby's set standard library was recommended for source reading. It was an awesome read! I think standard libraries are really good at demonstrating at least two things: the language's preferred coding style and implementation of data structures and algorithms using the language's primitives. For these 2 reasons, they're still worth reading, imo.