One of our current projects requires clean up of an ASP.NET application that has changed hands from one developer to another, has deviated from original scope and needs some tender love and care.  Brownfield application (re)development is challenging and time consuming.  Some things to consider when working on a Brownfield project are:

Never take any of the application code for granted.  The general rule of thumb is that if you'd didn't write the code, don't trust it!  Thus, an extensive review of the entire codebase is needed to understand what was attempted by previous developers, compared to the scope and goals set forth by the customer. Plan to spend a lot of time on Brownfield projects.  Since you're not starting from scratch, there's a lot of undoing/rewriting involved to produce a clean codebase.  Demonstrate small but measured successes to your customer.  Many customers are not technicians like ourselves.  These folks can't relate to the time we spend on rewriting classes, functions...

Silverlight 4, in my opinion, has matured to the point that it is ready for serious commercial-grade web applications.  The ability to create visually appealing user experiences coupled with all the goodness of .NET 4.0 is merged together now with the business world in Silverlight 4.  Development of my first Silverlight business application has been, at times, frustrating and, at other times, rewarding.  Coming from an ASP.NET background, I tend to look for things like master pages to streamline layout, and I still catch myself adding HTML tags to XAML and getting the red squiggly warnings. 

Here are a few things I've discovered thus far in my development process:

MainPage.xaml , for those of us coming from ASP.NET, equals master page!  That's right, this is the place to create your master layout.  In doing so, you can ensure that all the pages in your Silverlight application have the same look and feel. Use the Silverlight 4 Toolkit Especially Themes.  I chose BureauBlue for my first application as I'm prototyping an ASP.NET site that has the same branding colors as BureauBlue.  To ensure your style is applied to all pages, include it in the UserControl tag on MainPage.xaml.  Thereafter, all controls added to the page will acquire the Theme you've defined....