RadControls for ASP.NET AJAX 
RadAjaxManager, RadAjaxPanel, postbacks and ViewState are not supported
By default ASP.NET MVC view pages don’t have server form tag (<form runat=”server”>) which is required for ViewState and postbacks support. ASP.NET Ajax partial rendering is also not supported by ASP.NET MVC and as a result RadAjaxManager and RadAjax panel will not work.
RadCaptcha for ASP.NET is not supported
This stems from the fact that RadControls for ASP.NET Ajax depend on the ASP.NET Page and control lifecycle.
RadGrid’s built-in insert/update/delete, sorting, grouping, filtering, hierarchy or auto-generated columns are not supported
All those features rely on postbacks by default and as such are not supported in ASP.NET MVC. This blog post describes how to work around this problem.
RadInputManager is not supported
Because the input manager operates with MS TextBoxes with runat="server" attribute which is in conflict with the ASP.NET MVC concepts
Skin and base CSS files should be registered by hand when using the PartialView method
Alternatively you can use RadStyleSheetManager in the user control used in PartialView.
Updates via the built-in ASP.NET MVC Ajax support are not supported
The HTML of the controls is successfully updated however JavaScript is not executed by the built-in ASP.NET MVC Ajax implementation. We would provide a workaround in the future.
Only the ASP.NET rendering engine is supported
This stems from the fact that RadControls for ASP.NET Ajax depend on the ASP.NET Page and control lifecycle.