I got the updated version of the Pickaxe recently and skimmed through all of the 1.9 updates. I was appalled to see REXML is still the blessed XML parser. I liked it when I started using Ruby and I still see it in the wild, but to me that's usually the sign of old code or a developer not tuned in to the latest developments.

On the other hand, there has been some progress. It's good to see MiniTest replace Test::Unit (while also remaining mostly backwards compatible).