You stand correct. There is a serious gap between the design time experience between Winforms and WPF. But things are changing dramatically with VS2010. It has much greater design time support than VS2008. It is a matter of time till Telerik build the design time behavior for WPF and Silverlight controls to look at least as good as the Winforms controls. We will make the first steps in this direction with Q1.2010, and ofcourse will continue to improve it with the next releases.
Do you have any other feedback on the beta of the RibbonBar control. Are you experiencing any problems with it which we can address for the official release?
the Telerik team