File existence promise
I think the catch and then parts are unnecessary. A then accepts a resolve and reject handler, which you can treat a boolean.

var Promise = require("bluebird")
var fs = Promise.promisifyAll(require("fs"))

module.exports = fs.lstatAsync


Usage would simply be

var stat = require('yourFsStatModule');

stat('path/to/file').then(function(){
  // it exists
}, function(){
  // it doesn't exist
});