We are not planning to release a special suite build against .Net 4 for Q3 we will consider it for Q3 SP1. We made some fast test about the behavior of our controls in VS 2010. Here is what I found:
Controls are working as expected in both Silverlight and WPF except for where .Net Ria Services is used. You can read here
that Ria services are still not available for VS2010/ .NET 4. Because of that you can't compile the examples that goes with our installation as we are using .Net Ria. You can not start the exe for our example demos also. You can view them online on our site though.
WPF controls are automatically added to VS2010 toolbox but you can not add Silverlight ones.
So in fact you can use our controls in VS 2010 but it is not advisable and you may face some difficulties.
the Telerik team