Read it here: http://www.asp.net/learn/whitepapers/aspnet40/
Or download the whitepaper directly for offline reading here
Core Services Extensible Output Caching Auto-Start Web Applications Permanently Redirecting a Page The Incredible Shrinking Session State AJAX Functionality in ASP.NET 4.0 Client Template Rendering Instantiating Behaviors and Controls Declaratively Live Data Binding Using the Observer Pattern with JavaScript Objects and Arrays The DataView Control The AdoNetServiceProxy Class The DataContext and AdoNetDataContext Classes Refactoring the Microsoft AJAX Framework Libraries Web Forms Setting Meta Tags with the Page.Keywords and Page.Description Properties Enabling View State for Individual Controls Changes to Browser Capabilities Routing in ASP.NET 4.0 Setting Client IDs Persisting Row Selection in Data Controls FormView Control Enhancements ListView Control Enhancements Filtering Data with the QueryExtender Control Dynamic Data Declarative DynamicDataManager Control Syntax Entity Templates New Field Templates for URLs and E-mail Addresses Creating Links with the DynamicHyperLink Control Support for Inheritance in the Data Model Support for Many-to-Many Relationships (Entity Framework Only) New Attributes to Control Display and Support Enumerations Enhanced Support for Filters Visual Studio 2010 Web Designer Improvements Improved CSS Compatibility HTML and JScript Snippets JScript IntelliSense Enhancements Web Application Deployment with Visual Studio 2010 Web Packaging Web.Config Transformation Database Deployment One-Click Publishing Resources