With the release of the new Silverlight 3, a lot of new cool features have been introduced. One of my favorite definitely is the support of behaviours and triggers. In WPF the triggers are extremely powerful. They allow you to declaratively associate an action with an event or property value. In the previous versions of Silverlight one of the things that were really missing were the triggers and the behaviors. It was not possible, for example, to add mouse-overs to objects declaratively (as in WPF).