Ruby 1.9.1 supports the use of native threads and an implementation of fibers, and it is claimed that Ruby 1.9.1 is twice as fast as 1.8.7. This is great news for Ruby developers. However, it is warned that "unless you're dead sure of what you're doing, definitely do not expect to be using Ruby 1.9.1 as your production version of Ruby right away!", cautions Ruby Inside. They also mention that "a lot of libraries and gems will not work with it", and that "you'll see a lot of blog posts coming along in the next few weeks and months regarding efforts to bring existing libraries up to 1.9.1 standards".
Never-the-less, this is a great release for those programming with Ruby.