Although this is what should happen, it doesn't quite seem to be the case. Pretty much every other ruby implementation destroys Rubinius in terms of performance. It's also worthwhile to note that 1.9/YARV, which is bytecoded, destroys every other ruby implementation and should actually be a major boost to Rails once the compatibility issues are worked out (Matz released 1.9 during Christmas of 2007, but it's just the developer version). You can see benchmarks here:

http://antoniocangiano.com/2007/02/19/ruby-implementations-s...

You can also see how 1.9 fares against 1.86 directly in the code shootout:

http://shootout.alioth.debian.org/gp4sandbox/benchmark.php?t...

Rubinius seems to offer some nice support in terms of running reliable ruby (http://en.wikipedia.org/wiki/Rubinius), but in terms of performance and actual usability, it has a long way to go.