I'm not the first person firmly believing that validation should be mostly entity-based, not UI control-based. It's the object who must tell the system what kind of values should its field accept, user interface should only display this info. Microsoft Enterprise Library Validation Block was a serious step in the right direction, but uniform handling of data-based validation exceptions in user interface required quite a bit of custom coding there - just to make your UI know that the data was invalid.
Now, with validation attributes in System.ComponentModel.DataAnnotations namespace uniformly supported both in Silverlight (through .NET RIA Services) and in ASP.NET Dynamic Data, Microsoft makes even more serious step in supporting entity-based validation.
