The document discusses features of the ADO.NET Data Service Client Library in ASP.NET AJAX 4.0 including: 1) The library allows for CRUD operations on data from ADO.NET data services using a RESTful Atom Pub protocol through a proxy class. 2) CRUD operations can be performed through simple methods like query, insert, update, and remove which interact with the data service. 3) ASP.NET AJAX templates can be used to declaratively bind data from a data service to UI elements for one-way and two-way data binding.