In this post Vikram Pendse gives a simple and straight talk on Blend 3 Sketch Flow feature without any confusing technical terms and he also shares the right resources on net to refer.
For Designers, there is always challenge to build interactive prototypes for customers so as to give feel of application to customer in reality, Typically before tools like Blend Sketch Flow, we use to either build POCs (Again we need to put Man efforts in this activity) or we use to build designs in Excel or word, Drawback of this was, it does not helps to exactly put forth our point in front of client since they might not be that interactive and realistic which can give feel of application which we plan to build.