The smooth modifier provides you the tools to do smoothing groups, which keeps the topology unchanged but provides a sense of smoothing by manipulating the normals of the verts. Its a old modifier, found a reference to this modifier in an old help for Max version 4!
I have no idea if this modifier predates the presence of the same smoothing group function present in both editable mesh and editable poly object parameter rollouts, but it appears to be the same functions, just more than one way to get there. I suppose you'd use smooth modifier if you wanted the stack to give you parametric access to the unsmoothed model.
Opensubdiv and Turbosmooth both subdivide the mesh (ends up making lots of polygons). Opensubdiv is newer (at least in max) and has a lot of functionality. I made a 72 poly object, and applied opensubdiv, and got 288 polys. Applying turbosmooth instead of opensubdiv, and got 576 polys.
Probably Opensubdiv would be the place for your focus if your goal is organic shapes and you aren't on a tight poly budget. Its new, you can control the level of curviness via setting edge crease values, while with turbosmooth you have to create edge loops, which expands your poly count even further.
