Or for kind of wavy things like your example above, a brush based displacement type modeling program may even be a better fit than a sub-d polygon modeler.

You might want to check out Sculptris: http://www.pixologic.com/sculptris/ - that allows you to paint brush strokes onto a base object and then makes raised or lowered areas where your brush has gone over, it tends to be a better tool than NURBS modeling for doing organic lumpy type stuff.

Usually NURBS modeling is better for stuff that is somewhat more structured and is more defined by some set of profile curves. Things that are all lumpy and bumpy are not really very well controlled by just a couple of profile curves.

- Michael