I was in the Ruby land for quite some time and since TJH ported Sinatra.rb to Node.js under the name of Express.js, I learned Node.js and never looked back again - except I still love the Ruby syntax very much. PeepCode helped me learn and understand Node.js and of course, Dave Thomas' pragprog screencast, and eBook about Node.js.
So yes, I would say Node.js can do the same (or more) than Ruby + Rails.
But in contrast, Twitter switched from RoR to Scala. If you think about Spring, I assume you know Java. Maybe you could be happy with both paths.