MVC's RenderPartial in a WebForms page

We have a mixed ASP.NET MVC/WebForms application, slowly transitioning to all-MVC. Obviously, sharing components between MVC and WebForms is important to us.

Using WebForms controls in MVC views is easy enough (minus the postbacks), but when we rendered partial views in a WebForms page using Keith Henry's code we occasionally got evil "Validation of viewstate MAC failed" errors. Microsoft doesn't think hybrid WebForms / MVC apps are relevant, but then Mauricio Scheffer came to the rescue. Instead of having the partial views subclass ViewUserControl, we now subclass Mauricio's ViewUserControlWithoutViewState - problem solved.