Hi maxius,
You can also use Tgi3D SU Amorph plugin (http://www.Tgi3D.com) to create curved surfaces. It has also a free Training Edition with a limit on the number of vertices in the mesh. Below examples are created with the free Training edition, the resolution can actually go a bit higher but after a certain number of vertices in the mesh you would have to use the commercial version.
You simply select a closed loop and use “Create Mesh” command. This command creates the “smoothest” surface that fits the boundary. In the latest version, released two days ago, there is also an option to create “clean Bezier surface”. You would have to convert the boundaries to Bezier curves first. In the example below the one on the left is created with regular mesh and the one on the right is Bezier surface.
plane.jpg