in unofficial benchmarks with Rails (running different rake tasks and benchmarking them). 2.1.0 seems to be 20% faster than 2.0.0 and 2.0 was about 60/70% faster than 1.9.3 so that would make 2.1.0 about twice as fast as 1.9.3.
Pretty graphs here: http://www.isrubyfastyet.com/ (I run a nightly benchmark.)
I will add 2.1.0 right now and hopefully we will have confirmed data in the morning.
EDIT: You mention 20% improvement on Rake tasks. Simple Rake tasks are dominated by Rails' startup time. My benchmark reads about a 15% improvement in startup time, which agrees with what you are saying.
However, the 1.9 series was a significant step back from 1.8.7 for out-of-the-box Rails startup time. Ruby 2.0.0 pretty much matched Ruby 1.8.7. Now with 2.1.0, Ruby is finally categorically faster than 1.8.7 for starting Rails. (Rails itself has also made improvements; but my benchmark has been locked at Rails 3.1.3)
And, you were right, I put Ruby 2.1.0 live on one of my web apps last night, and didn't really get any kind of significant speed boost, what I did get was a significant decrease in garbage collection. here's the new relic graph, ruby 2.1.0 went live at 17:45 on the chart https://cloudup.com/ifosPh4rX4v
A micro-benchmark suite is better than a few micro-benchmarks, but really I would like a suite of real-world micro-applications.
I'm willing to add more benchmarks so it's not just Rails, but I simply don't know what to add.
Running with a more modern VM might yield better results.