The document discusses using Expression Blend and SketchFlow for UI prototyping. It describes how SketchFlow allows creating interactive prototypes quickly using hand-drawn sketches to get early stakeholder feedback, before significant coding work is done. This helps validate requirements and avoid redesign work later on. The document outlines SketchFlow's features like drag-and-drop interfaces, customizable controls and styles, and the ability to package prototypes for comment. It stresses aligning a prototype with user requirements and business goals.