I do a lot of CAD work.  I figure it takes a person about 40 hours to start using a CAD program or switch from one CAD program to another similar one.  It takes probably 150-200 hours to become as proficient in the newer, more powerful CAD program than the one a person is famliar with.

It becomes real interesting when one program is a familiar CAD program and another program with a different technique for CAM toolpathing and finally having to be familiar with two drawing programs  because clients use them and you have to 'fix' what they have so carefully designed so to be made.

Sketches and such are quite often done on paper or boards.  Once the design starts taking form, it is time to put it in CAD format. A drawign is done no faster in CAD than on a board with a competant draftsman.  Revisions are a lot faster and the drawings are more accurate.  Details are seldom redrawn but added from libraries of provious designs.  This assures more accurate completion of projects.  Or, repeation of previous goofy mistakes.  

In 1980 each engineer or designer had 5 to 7 draftsmen under them.  By 1990 a good CAD draftsman could keep up with half a dozen engineers/designers.  It also put another layer of manure between the designer and the builder.  Innovations of the builder are seldom carried back to design if there are many layers of orginization seperating them.

Well. enough of my rant.  Quite often someone will wonder how I can master a project using a saw and chisel when they have had problems with routers, power planes and the such.  I usually look at them, grin and say, 'first, one has to be smarter than the tool one is using.'

A lot of skills are learned, not taught and don't 'come natural'.