We have been developing rich internet applications using Silverlight for over 5 years now (since version 2).
We are skilled with Prism patterns and RIA Services having extended them ourselves to create very large Silverlight systems. These are fast to load and the plug-in-modularity allows for easy maintenance. Perfect for a team development environment. A pattern we strongly recommend is MVCVM, that is the inclusion of Controllers into MVVM.
At the moment we are helping a large UK company develop a medium-to-large scale Silverlight application using the latest Prism and MEF practices. Part of the task involved churning out multiple prototypes of the user interface. We used the much touted Expression Blend with Sketch Flow to produce 5 seperate iterations in less than a day each (most versions in only a few hours). To say the client was pleased with progress was an understatement.
We also investigated and solved the issues of local hosting of Silverlight web servers without an IIS server. This involved reverse engineering Cassini (the MS debug webserver) “a little”. The result is a self hosting Silverlight application you can serve up from any Windows PC (without IIS installed!).
If you have a need for rich user functionality, hosted in a web-browser, drop us a line.