Microsoft Sketch Flow is a brand new product that takes the prototyping to an all new level rightly being called by them as “Prototyping that works”. It is planned to be shipped along with Expression Blend 3.
The release candidate version can be downloaded from the following link:
Dwonload Microsoft Expression Blend 3 + SketchFlow RC
Sketch Flow helps the designers, account managers and information architects by bringing prototypes drawn on papers to life.
Sketch flow accomplishes this by adding flow transitions and animation to the sketches (That are imported in as scanned images) or to the product screens made inside of Blend using a wide range of hand drawn like components that can be dragged and dropped from the assets panel.

These working prototypes work like a charm to explain the entire high level flow of application to the client BEFORE the start of actual design phase.
The published project of this prototype can be sent to the client for review and feedback. The client doesn’t need to have Expression Blend Installed on their machines, the Sketch Flow projects only requires Silverlight browser plugin to work.
The client can review the prototype in web browser by navigating through very simple options. There is also a flow map available that gives the review of overall flow of the application.
The client can add the feedback in various forms on this running prototype using the text or highlight options available in the feedback panel of the Sketch Flow Player. This feed can then be saved in the form of a feedback file and sent back to the design team.
The design team can import this feedback file into their Sketch Flow project and all the client feedback is visible in the Sketch Flow Project inside of Expression Blend.
This is merely a surface scratch of the awesome features that Sketch Flow brings to the prototyping. I found a very interesting video in which you can see exactly how Sketch Flow adds value to your project.
Microsoft Visual Kitechen