I have noticed that the CTP of the Ribbon component does not support .NET 3.0. The application just crashes. This means it does not support Windows Vista out of the box.
Please consider implementing .NET 3.0 support in the final version of the Ribbon component. It should not be too difficult to implement since the changes in WPF from 3.0 to 3.5 are fairly minor.
If this is not done, I would have to use a 3rd party ribbon component or create my own, since I don't wish to alienate Windows Vista users by asking them to deploy .NET 3.5.