I have contributed to both - if you count patches, as I have no modules of my own in either. Also, one has to count projects linked from RAA, as it is not a repository of its own, that would probably be rubyforge that comes closest.

As your question is phrased I suspect that you think it might be "politically incorrect" for a Perl programmer to contribute to and therefore further Ruby, but I don't see it that way at all. Apparently you use both, since you ask, for whatever reason - suitability or curiosity perhaps. The only correct answer as I see it is that you of course should help making any of your tools better given the chance. Making either better at a task does in no way diminish the other, it only makes life easier for other people.

You will not hurt Perl in the slightest, but Ruby, which needs a bit more of a leg up when it comes to modules, could really benefit from some help.