The idea of creating rich interactivity without code should sound very appearing to designers, because we want to turn static UI into interactive prototypes and test out our design ideas quickly. In Blend 3, “Behaviors” are packaged, re-usable building blocks of interactivity. They can be visually applied to UI components in the application using drag and drop. No more opening up Visual Studio and writing routine code like starting an animation when a button is clicked. Blend 3 will have bunch of commonly used Behaviors shipping with the tool, but they are extensible so that you or your developers can create your customized Behaviors.
After watching Peter Blois’ MIX talk “Creating Interactivity with Microsoft Expression Blend,” I experienced the power of Behaviors myself in the tutorial below. For example, I used 3 different triggers( Mouse Click, Timer, and Mouse Gesture) to play the slideshow behavior. You can download many interesting Behaviors that the community are making at Expression Gallery page.
You can also download the video here.