Throughout the Interactive Designer CTP's and subsequent Blend 1 and Blend 2 preview releases, people from differing sides of the designer/developer roles have argued about what Blend is and who it is actually for. Maybe they only looked at it from their angle, without taking or trying to experience the other side's arguments and requirements. Either way, it is difficult to create a truly collaborative environment and, perhaps even more difficult, to implement the tools used to facilitate it. Expression Design, Expression Blend, and Visual Studio represent a real step ahead in the right direction to achieving this by speeding up the design/development process and allowing the original designers of a solution to maintain ownership of it.
Blend, used by a XAML architect, allows the collaboration to work in a real-world scenario, be it a small or large solution team. Only experience in working on WPF solutions will bring this requirement forward into discussions in future.
Blend offers you, the graphic or interactive designer, a way to decrease your delivery times while maintaining all your hard work throughout the solution development lifecycle and on to the end user. In other words, what you originally design is what you can now deliver instead of letting developers interpret and implement your visual requirements.
It doesn't mean you will never again need to use any of the tools you have used previously; it just means you will have the option to create, control, maintain, modify, and own your designs—instead of just hoping that someone else will.