> the pedometers require near constant use to be worthwhile
  > means that there's some degree of mental energy devoted
  > to them - is it charged, am I wearing it, etc.

That's what I like about my Withings Steel: it's just a normal (and beautiful!) wristwatch. I am wearing it everyday anyway. Actually I do not take it off, because it tracks sleep too. I am not worried about charging it, because it lasts for months. It looks like I get activity tracking as a bonus functionality. Much much better experience compared to some ugly dedicated tracker. Let's hope Nokia will not ruin it.