[jpedrosa]

I use JRuby to run a web application that I first coded in Ruby and it works pretty well even though it reserves and consumes more memory. Having a dedicated server for JRuby applications instead of running such applications on your own desktop alongside other applications slightly helps with the feeling of speed of the JRuby application, as it does not compete for CPU time with the other desktop applications you have like the browser, when you can feel that JRuby requires more work than Ruby for doing similar workloads. :-)

I know that the pros of JRuby for running Ruby applications mean things like being able to run multiple instances of Ruby from the same process, being able to run JRuby applications in a standard Java web-server be it as Servlet or a more high-level installation, and so on.

Also, Java has had a lot experience in running server applications so Java does help with maximizing the use of the resources available, be it 100% of CPU time, gigs of memory, multiple CPUs, and so on. Java has those famous garbage collectors and HotSpot technologies. JRuby can enjoy all of that so it does improve things over pure Ruby. Let's say, Java doesn't break a sweat under heavy load, or at least it shouldn't. Whereas with pure Ruby all bets are off.