Normal map from retopo is having artifacts, despite subsurf I did a retopo of a mesh by hand. Now, I found it to be ok and tried to bake a normal map out of the high-res-sculpt and the retopo. I tried it 


with one stage of subdivision applied
and without applied subidivision 


with subdivision it is smoother, but still has artefacts. now, if I subdivide further til the polycount reaches a supersmooth amount to blend out the polygon edges in the normal map, there is no sense in retopology I think? :S

(32-bit float-map, non colour data, combined with UV Map-node and Normal Map-node, linked to Diffuse and Material Output)



even with 2 subdivs, there are still minor errors:
This is due to a poor UV unwrapping (I guess you Smart UV unwrapped your mesh right?), UV maps seams should be hidden as much as possible. Search for UV unwrap 3D head on google to get an idea on where to cut.

Also read the Tangent Basis parts of this post to understand why your normal map create this kind of artifacts: http://wiki.polycount.com/wiki/Texture_Baking