I've heard this, but in practice it is hard to fully decouple the interface from the logic so experimentation with the front end usually involves work on the back end. Even simple changes like "we want to change this drop down to a set of radio buttons" ends up requiring changes on the back end most of the time.
I think good tooling support is a requirement for this to work; the one project I used this in (a Silverlight app) had first-class support for this. You could specify separate ViewModels for run time and design time, and the latter would just return static values that the designer could work against. I guess this would require some cursory understanding of C# syntax, but I think the ramp-up for adding/modifying a property would be minimal.
