Following the Telerik AJAX Product Support Lifecycle model (which closely resembles the Microsoft one), the time has come to retire the .NET 2.0 support for our AJAX controls. This will happen officially with the Q1 2011 release of the suite, slated in a couple of weeks, meaning that you will no longer receive .NET 2.0 versions of the Telerik AJAX assemblies, projects or VS 2005 integration as part of the installation packs. With this step the .NET 2 versions of RadControls for ASP.NET AJAX available in previous releases will enter their extended (paid) support phase as shown in the diagram from the linked resource above.
Since the .NET 3.5 and .NET 4.0 versions of the framework has been around for quite some time now and the public trends are that they are widely adopted already, we truly believe that this step will not cause you hassle. After all, if you are still not using the goodies from the latest versions of the .NET framework like LINQ, Entity Framework, ADO.NET and WCF services, etc., you should start doing so..