Here is a recent Torqbox (jruby jboss app framebork) benchmark article which also includes a comparison between Unicorn/Bluepill with Passenger3. http://torquebox.org/news/2011/03/14/benchmarking-torquebox-...
With a few rails apps under low load, Passenger3/REE/MRI1.9 works ok here. If load increases I'll probably look into possible alternatives and aggressive caching.