The benifits of Nurbs are in the smooth surfaces, relative speed, and the ability to convert your nurbs to any resolution of polys. Nurbs aren't often used for animation because it takes a lot of memory to get the exaactness of its smooth surfaces and then refresh it over an entire anim. So that's not so much a limitation of the style of modeling as it is our computers ability to cope. Believe me, if PC's (meaning personal computers) could handle the curves without problems, more people would start to use them but because they can't, cheating techniques like Subdivision Surfaces have turned up. They're a good blend between the speed of nurbs modeling and the light file sizes associated with polygon modeling. They can also be translated to a higher level of smoothness by adding detail only where you place it, unlike nurbs which creates a mesh with little regard of where the model is more detailed. Most 3D apps (most serious 3D apps) have nurbs or some form of nurbs technology included in their packages. Some, like Maya, started out being nurbs based packages but then incorporated polys as well because of their popularity. Once reality set in that nurbs wasn't for animating, polys once agian took the limelight and nurbs are now mostly used to compliment them ina scene, not replace them. Programs like Mirai, Maya, Softimage, 3DStudio Max, Rhino, Amapi and others use nurbs or have the option to use nurbs. I hope this helps.