Sure ... some of these have source code available, and some do not.

http://documentcloud.github.com/backbone/#examples

In particular the TileMill example (launched yesterday) is a really sophisticated map editing application, with annotated source code available, here:

http://tilemill.com/docs/models.html

(Use "Jump To", at the top right, to get around)

If you'd like to get your feet wet, and play around with models a little, try visiting http://www.documentcloud.org/public

Pop open a JS console, and try...

    Documents.length

    Documents.first().set({title: "Changing the Title Syncs the View"})

    Documents.first().set({description: "Lorem Ipsum Dolor Sit Amet"})

... then click on "Annotated Documents", at the top left, go back to the console, and try:

    Documents.first().notes.fetch()

    Documents.first().notes.first().set({content: "Writing a Note."})

You get the idea.