I started backend development with Nodejs because I was familiar with JavaScript. I dropped sails after a month because of the lack of documentation and help available when something went wrong.
A few months later I happened to try Rails and realized that that was what Sails was trying to be for JavaScript. At some point Sails will become awesome, but until then I'll stick with Rails.
Sails.js, Meteor.js, and etc... are frameworks that use/run on Node.js.