[dham]

> (1) if you are expecting a lot of load you will likely get more throughput out of the JVM

This is true but not really a reason to move away from Ruby. We've found a really good medium between doing Rails on MRI and writing Rack services with JRuby and Torqubox when we need a lot of throughput.

>(2) You may need to use a particular JVM library (there's a lot of really good ones).

Honestly, this is more of a reason to stay on the Ruby/Rails side instead of the JVM side. In Rails there are libraries that can help you with anything dealing with web applications. I've been in the Java ecosystems: Play Framework, Spring, and Java EE(JSF), and I have never seen anything like the Rails ecosystem. It allows you to iterate much faster on a project. The JVM never really attracted me(on the web side) with it's libraries. We do however use JFreeChart which we use as a fallback to javascript charts, because it outputs an image really fast. For that Rack and JRuby are enough though.