When working in 3D I often find it easier to construct new objects on the WCS, then manipulate them into place afterwards. Placement can still be a bit of a task, It would be nice if you could simply MOVE or COPY them relative to the DUCS. I recently realised that I could do this by levering off the fact the INSERT command works in respect to the DUCS, and created some LISP to take advantage of this.
The Forum doesn't seem to be uploading images at the moment, so have created a post here with some graphics to illustrate what I mean.http://www.cadconcepts.co.nz/news/copy-or-move-relative-to-ducs/
The attached LISP has two commands, COPYDUCS, and MOVEDUCS. It is also useful to remember when using DUCS that the alignment will change depending on which way you move your cursor onto a face. Also that you can lock your DUCS by pressing the Shift key.