Hi Pieter,

> Is there any article explaining how the splines are weighted?

http://digiitalarchfab.com/portal/wp-content/uploads/2011/03/Nurbs-Curve-A-Guide-for-the-Uninitiated.pdf

but it's pretty math heavy. Weights are primarily used in NURBS modeling to get exact conic sections like arcs, circles or ellipses.

Usually the main technique to get pieces to align is to construct them from a common base curve, not to manipulate surface control points like that.

Also as others mentioned using booleans and trimming is usually the main strategy to target rather than something to avoid like it is in polygon modeling. Another facet of this is often times it's good to build things out of longer extended pieces and cut pieces away rather than building a surface directly to some complex boundary. So it's really quite different.

There are some tips for people coming from a poly modeling background here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael