The Validation Application Block (VAB) added to the Enterprise Library v.3 a comprehensive set of common validators and integration adapters for Windows Forms, ASP.NET, and WCF. Additionally, Martin Bennedik built an adapter for WPF. More than half of those who responded to my EntLib Extensibility survey, indicated that they used VAB. That's a great adoption!
If you are using VAB with ASP.NET, the server-side validation requires a full post-back and results in some performance depreciation. Now you can improve responsiveness of your Web apps that require such validation. Patterns & practices Web Client Software Factory team just released the Validation Guidance Bundle. It leverages VAB and ASP.NET AJAX to perform server-side validation without doing full post-backs. It’s pretty easy to use. The bundle also includes recommendations on which validation types to use for various scenarios and a good demo that leverages a mix of validators both on the client and on the server.
All in all, if you are building Web UIs for your business entities that are already validated with VAB, you’ll find this bundle quite useful!