Scott Hanselman has a great overview post up on ASP.NET Dynamic Data. It's a new preview ASP.NET framework that works with .NET 3.5 which allows you to mark up your business objects with meta data that will be used by your GUI code to control what type of control is used to view and validate your data. This is huge if you have multiple screens that show the same data points in multiple ways, because it allows you to centralize this code into your business objects so that you can change your visualization in one location, and have it spread across all your pages. Wow!
Now the only question I have is why doesn't something like this exist for WinForms or XAML? Or does it already exist and I just don't know it?