Overview
underscore+ is just a thin wrapper over underscore + mixins
Use where traditional underscore would be used...
var _ = require('underscorePlus');
_.map(array, function(el) { }); // from 'underscore'
var str = _.sprintf("%0.2f", float); // from 'underscore.string'
Underscore Documentation
Underscore: http://documentcloud.github.com/underscore/
Underscore.string mixin: http://github.com/epeli/underscore.string/