Hi Niko, could you please point out which things you are using as rails and which things as profiles for the sweep, and also what parameters you are using in Rhino?

But one thing to be aware of is that it is pretty normal to have creases between things if you build them in individual chunks, see here for a description:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1398.19


If you want to have smooth things, you're usually better off building them as larger surfaces instead of as cut up strips.

- Michael