Project Scene Graph provides an interesting alternative to Swing for designing interactive user interfaces that can take advantage of animation and effects. Although you could accomplish the same tasks with Swing, you would need to create the equivalent of Project Scene Graph (at least the animation and effects portions). What would be the sense in reinventing the wheel?
Project Scene Graph isn't a replacement for Swing. Instead, you can create some interesting hybrid user interfaces that involve Project Scene Graph and Swing—you would undoubtedly develop the RIA part of such a user interface with Project Scene Graph and develop the non-RIA part (configuration screens, for example) with Swing.
Where do you go from here? One possibility is to investigate the various Project Scene Graph demos (such as an egg timer, a calculator, and even an iPhone-like user interface) at the Java.net-hosted Project Scene Graph: Demo Gallery project page. These demos will help you learn more about this technology.
Another possibility is to explore JavaFX, which is based on Project Scene Graph, and which offers a higher-level approach to user interface design than Project Scene Graph can provide. If you're interested, visit the official Javafx.com page to learn about JavaFX and download a JavaFX software development toolkit.
What does the future of Project Scene Graph look like? For an answer to this question, I recommend that you read the response to a similar question posted here. Although the response offers only an opinion, the opinion originates from Project Scene Graph developer Chris Campbell.