An interesting case occurred in Japan. The young teenager who participated in the Security and Programming Camp 2009 in the summer, under the guidance of a teacher, worked to improve the performance of Ruby 1.9. The successes achieved by him can be called excellent, and if you take into account age, it is amazing. The teenager was able to speed up the execution of some Ruby 1.9 methods (which, I recall, is famous for its performance relative to version 1.8) by an average of 8%. The maximum acceleration was even 63%.
The link is small details of what the teenager did. His work focused on loop optimization and getting rid of unnecessary macros. The patches of the boy were taken on October 5 of this year into the Ruby trunk.