Well you would use nurbs to make smooth objects like fancy cars, I think. I wouldn't know really what people use nurbs for these days, I'm a newb too so I guess for simple objects, who don't need the level of control you require with poly/sub-d modeling.
People used to use nurbs to do organic modeling afaik, but with the introduction of sub-d's people switched over to polygonal modeling, since this form of modeling allows more control than nurbs modeling, but still has the same quality.