In the next part of his Jounce series, Jeremy Likness diggs into Visual State Manager and transitions.
Source: C#er : IMage
One of the most common questions I get about Jounce is how to handle transitions, since the ContentControl immediately swaps out content. There are some third-party solutions, such as the TransitioningContentControl from the Silverlight toolkit, but Jounce can also handle this right out of the box.