I just came across this article by way of the Smart Client Data blog.  I have had quite a few conversations with customers about building occasionally connected smart client applications.  Smart client applications work whether connected to the Internet or not. Microsoft® Money and Microsoft® Outlook are two great examples. Smart clients can take advantage of local caching and processing to enable operation during periods of no network connectivity or intermittent network connectivity. This functionality is extremely valuable in this new era of mobile information workers especially given the cost, latency and speed of mobile connections.  SQL Server Express is a nice option for your local data store.  You can find the article at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnsse/html/EmSQLExCustApp.asp.

-Marc