Not so much a hint or tip - more an experiment.

At Flash on the Beach this year, James Paterson was one of the inspirational speakers. During his talk he showed off a novel 3D sketching tool (well, novel to me, anyway) which let you sketch a pen line on a 2D plane, then rotate, and sketch again, adding another plane to your scribble.

I believe it was written in C or C++ (from memory).

I thought I'd have a quick go at doing something similar in Flash using Papervision. So here is a very rough copy. Not nearly as polished - or as fast - as James's, and doesn't have the nice line-intersection-with-drawing-plane feedback that he had, but it works as a quick proof of concept.

You can try it out here:
http://code.awenmedia.com/source/scribble/Scribble.html