Why Use Scala?
Why use Scala when you have Ruby and Ruby on Rails? Well, we still use Rails. It works great for front-end stuff. The productivity is worth the tradeoff for working in a slower-performing dynamic language. When you think about what a web framework is doing under the hood, itÂs tons and tons of string concatenation. Ruby on Rails can handle that.
What we had a need for as Twitter grew was for long-running heavy processes, message-queuing, caching layers for doing 20,000 operations a second. Ruby garbage-collection is tough, Ruby doesnÂt do really well with long-running processes.
http://blog.redfin.c...r_uses_scala.html
Do some searches on Scala and Twitter. I agree with Scott, the servers must do a shared-nothing approach and they probably won't use the back-end of Rails ORM as much (ActiveRecord).
Have fun.