We try to do as much of the house’s repair/maintenance work ourselves as we can; it saves money, I have (fortunately or unfortunately) the time, and I enjoy it. I probably don’t do enough of it. There are, to my way of thinking, three types of work arranged on a sliding spectrum of required focus: the intense physical/mental work that demands all of your attention: this might be using a chainsaw or doing research, in either case that is what you are doing, thinking about something else shouldn’t be happening. If you are thinking about something else, the work is not being done. At the other end of the spectrum there is the truly repetitive work that needs only minimal attention, not much really falls into this category, if only because minimal attention usually ends up with minimal results, some assembly line work is probably the closest, where the same action is simply being repeated.
Then there is the middle. In some cases the work being done is boring and really can’t be improved on, maybe because you have reached the highest level of skill the job needs: mowing the lawn, vacuuming, cleaning stalls…you can only get so good. You need to pay attention, but not really focus. Those jobs give you plenty of time to think, observe, work on something else; I wrote many essays in my head cleaning stalls. In other cases, you can always do it a little better and because of this the job becomes a challenge (eventually the challenge is great enough to move it into the first category). I encountered the prospect of a mild challenge the other day, reputtying some old, very old, windows that are being used as a cold frame. Because the glass is old, I wanted to ensure that it was solidly in the frame, so those windows got the same treatment that a window on the house would get. The added advantage was that because they aren’t on the house, no one will see them, and so it was a great opportunity for improving my technique. Setting my mind to a task that was not exhausting, but did call for attention to detail, experimentation, and kept my hands busy resulted not only in a pleasant few hours but also let me think about an article I needed to have written. Doing some chain-stitch embroidery the other night also had the same effect.
One sort of wonders then, so many times you hear of an author being admired for managing to write despite being busy with their other jobs. But did their jobs give them the distraction that allowed them to write? If they had nothing but free time, could they write? (some can and do of course) Julie was a prolific writer, how many of her books, I wonder, were written while sewing?
Acair Fearann 
You left out the “total immersion” jobs: those into which you submerge yourself and eventually come up for air, hours later, and look around for awhile to re-place yourself in the present universe. This involves much, much more focus of attention – whole body/mind attention – than even wielding a chain saw. Writing, for me, often falls into that category (once it has exited your middle level category). Judging from the bit I’ve read of Julie’s books I’d guess that her involvement varied from “This is happening on auto-pilot” to total immersion.
I did leave out total immersion, perhaps because it is so hard to explain why writing or research, the latter especially for me, is so engrossing that not only do hours pass but that in the end you realize that you are Absolutely freezing because the archive is kept at 55 and you haven’t moved in four hours. Rather difficult to comprehend how reading (!) could make one routinely ignore the physical world without the been there, done that stamp already in place.
I didn’t know it was possible for you to achieve a state of “absolutely freezing”!
Someone should study the physiology/neurophysiology of the “total immersion” state; I wonder how closely it might relate to, say, “ecstatic” or “meditation” states of the mind and body. It certainly is a good place to get to – and I think a uniquely human one. (A cat trying “total immersion” in front of a potential mouse hole will just fall asleep. . .)