Here you can download new Solaris Express bits. Dan Price has blogged about new features in this release. In his previous blog entry you can find What's New for 2/03 release. Both releases have features and bug fixes which are not in Solaris 10 (yet). So if you want to try with latest Solaris bits SX is a way to go.
btw: some bug fixes or features in this release are result of my own BUGs or RFEs I sent to Sun. It's nice to see that Sun is really listening to its customers. And it's not the first time Sun fixed a bug or implemented RFE I requested.