I was in a similar position to you a little while back. I found the annotated source of the TODO app on DocumentCloud a good start. I then found it was worth spending the money on Recipes with Backbone by Nick Gauthier & Chris Strom.
That being said, I've always found the best way to learn, is to do. Come up with an idea for an app and build it using Backbone, with the help from the resources above. You'll learn a lot.
http://documentcloud.github.com/backbone/examples/todos/inde... http://documentcloud.github.com/backbone/docs/todos.html http://recipeswithbackbone.com/
That being said, I've always found the best way to learn, is to do. Come up with an idea for an app and build it using Backbone, with the help from the resources above. You'll learn a lot.