The Ultimate ListBox for SIlverlight can be used within a Silverlight 5 application, but you will need to include the System.Data.Services.Client (sdk) dll. This is not the case with Silverlight 4. We have not yet made decisions if we will have a native Silverlight 5 component or advise our clients how to include our components with Silverlight 5. I believe these announcements will be made this year. The reason why it has become slightly difficult to make these changes is that Xceed will also need to wait for more information concerning Windows 8. Xceed will also need to investigate about the new .NET framework (4.5) and its impact on Xceeds components. This information should be posted on our website, but you will find out sooner rather than later.
Developer in Technical Support
Xceed - Multi-talented components - http://xceed.com