Sketch on non planer surface (new feature sp2)

[AP23]

Autodesk has included a new feature where you can sketch lines on a curved surface which adapts to the curvature. A very welcomed feature, however it has a few limitations. You can't sweep anything on the curves. You can't extrude them either. I guess there were only made for the new conceptual sustainability feature.

http://autodesk-revit.blogspot.com/2010/10/revit-2011-sketch-on-non-planar-surface.html