I've been using the New York Times reader as a great example of a smart client, of the power of WPF and an example of integration with the platform for some time and have been promising for ages that we'll release an SDK allowing you to take advantage of the things we discovered while helping NYT to build it. Well, we finally have. Grab the SDK from http://windowsclient.net/wpf/starter-kits/sce.aspx and knock yourself out. As Tim says,
... potential to go beyond a news reading scenario and handle other kinds of data synchronization and display needs. For example, you could use this as the basis of a client for financial data analysis, where the application downloaded stock prices and other financial information and presented it in a rich client experience.
The potential for this kind of app is huge. Remember, connectivity is not a boolean property.