Integration of Node.js and Backbone.js
This is a good tutorial that shows how to setup that entire stack.
http://backbonetutorials.com/nodejs-restify-mongodb-mongoose/
In short...
Node.js
You can use a library like restify to provide a restful API for your client-side Backbone application. It can also serve your static assets for your Backbone application. The example uses restify, but could be accomplished with other libraries like express.
Mongoose
Mongoose is a javascript abstraction layer for MongoDB. This provides an easy way to interact with MongoDB from Node.js.
Backbone
Your Backbone application can utilize your restify node.js backend to handle the model synchronization. You should have plenty of control to setup the routes via restify in a way that makes Backbone happy.
This ebook could be useful (it's on Backbone, but uses Node for the backend):
http://addyosmani.github.io/backbone-fundamentals/
You also may want to look at this book:
http://www.amazon.com/Building-Node-Applications-MongoDB-Backbone/dp/1449337392
There is also Node Cellar Source.
There is not much explanation about the code, but the app is simple enough to get started and understand the basics layouts of node / backbone
It is, i think, just between an 'Hello World' code and a full app.