2. Silverlight and WPF share same syntax, code and libraries.
2. WPF competes with Windows Forms only for writing desktop applications while Silverlight competes with Flash, Java web apps etc.
Consists of a XAML and a code behind file
Cannot be styled/templated
Derives from UserControl
Consists of a code file and a default style in Themes/Generic.xaml
Can be styled/templated
The best approach to build a control library
Update: For Part 2 of this post, click here.