There's a some stored wisdom about doing reverse-engineering with Rhino on their wiki:
http://en.wiki.mcneel.com/default.aspx/McNeel/ReverseEngineering.html

Specifically the Scan, Cleanup, Remodel whitepaper linked at the bottom is pretty good.

However, if you're coming from SubD, it's probably easier to convert the control cage directly to Nurbs rather than getting a subdivided model and doing reverse engineering. It'll be a lot faster, generally better looking, and your Nurbs will have the same isocurve flow as the original SubD.

There are a few programs that will let you do the conversion from the control cage directly to Nurbs. There's Maya, Catia's imagine and shape, and T-Splines for Rhino, that I'm aware of.

I'm a developer for T-Splines, so I'm a bit biased, but I think you'll get better output from any of those than from manually reverse engineering.

Hi Tom. Amapi can do it too, but it always died on me at around 100 polygons. On the contrary, I once converted a mesh in early TSplines beta with more than 80,000 faces. That was before you added the fancy smoothing code... :)

jonah

Thank you for the links and the answers to my questions !
I will look into it ...
Peter