Asynchronous event driven API that leads to high scaling and lower memory footprint, we all know that (The now famous C10K problem). I have used EventMachine in Ruby and it always felt like working against the grain in ruby. Blocks typically are thrown for instant execution and rarely as a callback. The lack of Fibers in Ruby 1.8.7 does not help. Turning non-evented ruby code into evented ones is mind-bending exercise till you get it.
There is some serious innovation happening around Node.js. Some are being built over experiences of other Languages. There is no such thing as Rails for node.js (which I consider a smashing thing). Most people use Express which is similar to Sinatra. Coffee script became popular because of and in the Node.js community. Now the Rails community is trying to make coffee script the default . RVM became popular only in recent times in the Ruby Community, We already have NVM doing the same thing for node versions. I can’t forget to mention the fantastic Socket.io for realtime push applications and it is truly trivial to use.
The mushrooming of cloud hosting for node.js is also a proof that a lot of vendors think it’s interesting. Just off the top of my head, there is Joyent’s no.de, Cloudfoundry, Duostack and Nodester all in some sort of beta stage. Although from my brief experiments, I prefer the CloudFoundry to no.de and Duostack.
And Rails definitely does not have a rap theme song as cool as this. http://soundcloud.com/marak/marak-the-node-js-rap. (Listen with headphones, please)