With Composite Application Library (CAL), you can only adopt the components your application requires. For example, you could change your communication approach from .NET Framework events to use the Event Aggregator, which allows you to send loosely coupled messages between modules.
Composite Application Guidance

There are a few huge wins for a customer when you build your line of business application this way:

1. The initial load isn't as large - you can have a quick load of a login and common UI, then as the person logs in, prepare their environment by loading additional components
2. You can show a quick "Do you know… you can do XXX" while this is loading. You can also show them a quick list of what has been happening (e.g. a Dashboard).
3. You can also implement special cases where perhaps HR and Finance both use the same area, but with different customizations. So based on who logs into the system, Silverlight can dynamically load a different assembly giving them a different behaviour.
4. You can also build simple "Plug-in" like functionality, allowing simple customizations of your application based on your own published interface API.

This works really well with Silverlight's Application Caching as well - and lets you build and release different component modules separately.

You can find out more about Silverlight's Dynamic Assembly Loading here:

Thread.Sleep(5000);
this.Dispatcher.BeginInvoke(new Action(() =>
                            {
                         //Try to reconnect in the background
                               Connect.Execute(null);
                             }));
Bad: Using Thread.Sleep() causes your Silverlight application to freeze 
 
 
Storyboard sb = new Storyboard() { Duration = TimeSpan.FromSeconds(5) };
 
sb.Completed += (ds, de) => this.Dispatcher.BeginInvoke(new Action(() =>
                                                                       {
                                                                          //Try to reconnect in the background
                                                                         Connect.Execute(null);
                                                                       }));
sb.Begin();
GOOD: Use a Storyboard with a duration of the delay and once the Storyboard is finished running

An application can now be easily found on the user’s desktop or start menu, and launched with a single click. However is not easy to do, the main difficulty, is that you do not have the HtmlPage object, so if you were relying on IFrame pop up or javascript, or if you are using Silverlight's navigation framework (e.g. silverlight.aspx#Contacts/JohnDoe).

Figure: OOB demo from  http://www.microsoft.com/silverlight/out-of-browser/demo/

The most important aspect of WPF or Silverlight that makes MVVM a great pattern to use is the data binding infrastructure. By binding properties of a view to a ViewModel, you get loose coupling between the two and entirely remove the need for writing code in a ViewModel that directly updates a view. In a sense, Views and unit tests are just two different types of ViewModel consumers. Having a suite of tests for an application's ViewModels provides free and fast regression testing, which helps reduce the cost of maintaining an application over time.
A good article about MVVM

Mobile Device:


    Figure: Silverlight does not work on an iPad, It can't be only experience. 
     Further Reading: PCWorld  .