Absolutely - as much as I wish she wasn't, our toddler is currently hooked on the equivalent of 'unboxing' vids on YT ('surprise eggs', if you're curious). We limit her time watching, of course, but I still have to keep an ear open for ads kicking in. I'd certainly pay.
Wow. I knew it was cheap - that makes sense in light of what you're saying. Though there is a minor sting: "mobile networks charge each other interconnect fees of at least US$0.04 when connecting between different phone networks" [1]
It started as an itch to scratch: I was being asked the same or very similar questions again and again by friends and colleagues, so I decided to package it up.
Wrote it all in Markdown. Tried Scrivener, but didn't get on with it, so went with my code editor.
Writing took longer than expected, because it was done in the time around helping with my then-newborn daughter, so it's tricky to tally up how much time I actually spent on it.
I'm a former journalist and editor, like my wife, so shaping and refining the manuscript was straightforward, with her second set of eyes proving invaluable. However, useful advice for anyone, regardless of experience, is: set a limit on the number of drafts/reads/edits you do. When you hit it, publish, rather that get trapped in Edit Valley. (And with self-publishing, it's easy to push out updates, after all - particularly with Leanpub).
I've actually done very little marketing for it. Google Adwords didn't prove cost-effective for me, so sales have mainly come via word of mouth/blog posts, HN, Reddit and the like.
FWIW, in the first two months, I made more from the book than the advance was on some print, publishing-house books I was asked to write when I was a journalist (but I turned down).
It's still ticking over fine at the moment, but (in terms of boosting sales) I should really make time to do a big revise-and-expand v2, rather than the incremental tweaks I've been doing. At the same time, I still believe it's relevant and useful as is, so I don't mind keeping my time clear for family, other projects, etc.