CSS layout is awesome, except when your layout calls for a header, a footer, and columns in between. Use float, and content changes can cause columns to wrap. Use absolute positioning, and your footer can crash into your columns. Add the complexity of drag-and-drop layouts, and a new technique is needed. Enter "faux absolute positioning." Align every item to a predefined position on the grid (as with absolute positioning), but objects will still affect the normal flow (as with float).
The rise of Ajax and rich internet applications has thrown the limitations of traditional wireframing into painful relief. When you leave the world of page-based interactions, how do you document all but the simplest interactions? Flowcharts and diagrams don’t work. Prototyping saves the day by focusing on the application and conveying its "magic." Prototypes can help you sell a decision that is fundamentally or radically different from the client’s current solution or application. Sit a stakeholder down in front of a working prototype and show him or her why your approach is compelling.