This is a glorious day! Joni (Marcin's incredible Java port of the Oniguruma regexp engine) has been merged to JRuby trunk. It seems to work really well right now.
I did some initial testing, and the Petstore numbers are more or less the same as before, actually. This is explained by the fact that I did the integration quite quick and tried to get stuff working without concern for performance. We will go through the implementations and tune them for Joni soon, and this will absolutely give JRuby a valuable boost.
Marcin is also continuing to improve Joni performance, so over all this is a very nice approach.
Happy merge day!