If the question here is How to learn Backbone, my suggestion would be to take one of the to-do app examples and just build and hack on that until you develop the app you want. Try doing it with just built-in backbone functionality; don't override any of the defaults. Use hacking an already built-app to get a feel for the limitations of the framework, which in turn will show you some interesting (for me, at least, coming from MVC world) design patterns.
If the question here is Where is a good Backbone tutorial, I encourage you to look at the tutorial on Backbone-Relational (which is a plugin for Backbone):
Yes! Coincidentally I was using that tutorial to learn backbone yesterday morning. I found it was a great all-round illustration of how everything ties together. One thing I found quite lacking in other tutorials was how you wire up your front-end backbone app to backend web services. This tutorial demonstrates how you do that very well.
Totally sympathize with that difficulty. If you have access to Safari Books Online, they have a really good chapter that also goes through the Backbone wiring-up process in their MongoDB book (which has a chapter about Backbone).