I quickly implemented the benchmark they give using RubyJS. It takes 11.57 seconds in HotRuby but only 4 seconds in RubyJS. The same benchmark executed in Ruby 1.8 takes around 24 seconds!!! But only 0.12 seconds if you replace the “+=” by ”«”, so I consider this a very bad benchmark because it only benchmarks the performance of String allocation in the underlying VM/interpreter and not that of RubyJS/HotRuby. A benchmark with a lot of method calls, as is usual in a regular Ruby application, would be a much better benchmark. I think this would show even better results for RubyJS.