Some general notes on the whole "Essential Skills" post.
A couple of commenters mentioned that it is a bit heavy on electronics. True; partly that's because I'm an electrical engineer, but it's also because, in my experience, it's also where many makers (aside: I will continue to use that term; I came to my personal peace with it during the discussion about what to name the Twin Cities Maker group) "fall down" and lose confidence or run aground. Electronics is a massive sphere, and my hope, by including those things on the list, was to encourage people to develop familiarity with the most basic, most useful aspects of it (at least, as far as general making is concerned), rather than feeling overwhelmed by the whole thing and steering clear of electronics projects altogether. Some of the coolest projects I've seen were banged together by people with little or no electronics experience, just the confidence to go forward and the willingness to make a few mistakes.
In the intro to the list for the BoingBoing crosslink, Cory Doctorow invoked Heinlein's "Specialization is for insects" mantra. I'll admit that I'd forgotten about that, but it was the spirit in which I was writing the list. Some people made suggestions later: rebuild an engine, wind a motor, weld, etc. I avoided things like that, because they tend to be too specialist. My goal for this list was to include nothing that required more specialized equipment than one was likely to find at, say, Wal-Mart. I think part of the maker "movement" is a sense that vast outlays of material and equipment cost are not and should not be required to do remarkable things. Welding, rebuilding an engine, using an engine lathe or a vertical milling machine, these are all admirable (and valuable) skills, but they are also out of reach for a vast swath of the making public. Most everyone, on the other hand, can find room (and money) for a tote box that contains a Dremel tool, an assortment of glues, a soldering kit and a multimeter.
Over the coming days (and weeks, no doubt), I'll make one post about each of the items on the list, and probably an updated list, too- I have no doubt some of the commenter's suggestions will make it on (and credit where credit is due, of course).
I hope some folks will check up occasionally and see what I have to say.