I'm not sure what your definition of "reusable" is, exactly, but most of the examples are completely reusable with only minor changes. The autosuggest textbox, for example, can be reused completely by just changing the suggestion provider, which has a very simple interface.
All of the examples in the book were made to show you basic concepts and give concrete examples that you could get working on your own to play with. Perhaps what you're really asking for is a framework to build functionality? In that case, then the examples in the book wouldn't suit your purposes.
Nicholas C. Zakas