Antonio Cangiano has updated his Great Ruby Shootout because of an interesting finding (emphasis mine):

The really big, flashing warning though is what happens when you install Ruby through apt-get. Compiling from source gives you double the speed, according to these tests. I expected a 10/20% increase, not 100%. The gist of it is that prepackaged Ruby is compiled using the option –enable-pthreads and there is the whole issue of shared vs static libraries. But whatever the reason, this is a significant difference. For production use, in light of these results, I feel that it would be foolish to use the slower version of Ruby provided by apt-get/aptitude.