Thank you for the nice words on our new products and features.
In regards to the term "Beta":
This is the first public release of the new "Prometheus" controls and we are very eager to hear your feedback. We completely support the new bits and we are confident that they can be used in production environment. We are giving dev licenses to all Telerik subscribers and are encouraging customers to start playing with the new controls. It is also perfectly safe to start mixing the "Classic" ASP.NET controls and the new "Prometheus" controls in your apps -- a good course of action is to start incorporating them in some existing apps.
We are very serious about backwards compatibility and we will do our best to not break this code for the upcoming beta updates towards the official release. The core framework is quite stable and we should be safe to upgrade it with new ASP.NET AJAX controls (Grid, Editor, Menu, Scheduler etc). Backwards compatibility is our top priority and we will have primary focus on that.