I have heard many customers ask about building business applications on Silverlight... the union of a great .NET programming model web-style deployment\update and rich user experience makes Silverlight an attractive option. 

Rockford Lhotka recently released an update of his very popular business application framework CLSA.NET for Silverlight 2! 

You can read the over view here:  Overview of CSLA .NET 3.6 for Windows and Silverlight 

While we are at it, the Patterns and Practices folks are also working on Prism for Silverlight... another great resource for you!