I reverted to 1.8 because I could not find documentation for the Standard Library of 1.9. Generating it myself also proved impossible (out of memory errors and other issues).
http://www.google.com/search?q=site%3Aruby-doc.org%2Fcore-1....
There's the documentation for the Array class, but you can't get to it from the 1.9 core documentation:
Here's a decent source for ruby 1.9 docs, though:
http://rubydoc.ruby-forum.com/
Ta-da!
I know it is also a gem and as such the documentation for JSON can be found. But I would kind of like to have the official 1.9.1 standard library. Also because some things changed from 1.8