In my tests, Ruby 1.8.7 runs simple benchmarks about 3-8% faster than 1.8.6 – that’s nice!
But Ruby 1.9.1 is far more fast, with speedups up to 2x for some real-life cases, and a reliable speedup around 10-20%.
JRuby performs better than 1.8, sometimes even better than 1.9, but only for longer tasks. For short benchmarks and day-to-day tasks, it’s often 2 or 3 times slower than any C-Ruby. The startup time is around 1 second, and thus JRuby is not the right tool for scripting tasks. It runs best on Java 6.
Compared to Python, PHP, Perl etc., Ruby feels equally fast to me. That is, well-written Ruby code can perform as good as well-written code in any other dynamic language (with the exception of OCaml, maybe). Bad-written code is no benchmark at all.