Kendo UI for ASP.NET MVC is the successor of Telerik Extensions for ASP.NET MVC. Telerik Extensions are in a maintenance phase and will be actively supported (bugfixes and minor enhancements primarily) till Q2 2013.
You can easily migrate existing projects as Kendo UI for ASP.NET MVC is comperatively identical to Telerik Extensions. In fact, it has been built by the same team. Both products can be used side-by-side during your migration. And if you need help, our renowned support team is here for you.
Telerik MVC Extensions Support Resources
Online Demos
http://demos.telerik.com/aspnet-mvc
Documentation
http://www.telerik.com/help/aspnet-mvc/introduction.html
Code Library
http://www.telerik.com/community/code-library/aspnet-mvc.aspx
Telerik MVC Extensions Suite
http://www.telerik.com/products/aspnet-mvc/extensions.aspx
FAQ
http://www.telerik.com/products/aspnet-mvc/getting-started/mvc-kendo-faq.aspx
Migration Guide
http://www.kendoui.com/documentation/asp-net-mvc/migrating-from-telerik-extensions-for-aspnet-mvc.aspx
Migration Blog Post
http://blogs.telerik.com/aspnetmvcteam/posts/12-05-31/kendo-ui-for-asp-net-mvc-and-the-telerik-extensions-for-asp-net-mvc.aspx