My colleague Brian wrote a vtkBezierSurfaceWidget that can work with vtkBezierSurfaceSource to help users in interactively manipulating the control points of a bezier surface; and hence manipulating the surface. If you checkout from the SVN, you can find both these classes in there. Take a look at the video below.
If you cant see the video embedded in this blog, then click here: http://www.youtube.com/watch?v=uYtOTmytK9M