Looking at Matt's instructions, wouldn't that seam down the bottom of your foot (and right up the back of your heel) be uncomfortable?

The pattern link seems to show a more complicated but perhaps better constructed version, with an attached sole.

Comments or feedback about comfort from anybody who has actually worn them?

I'm wondering about a spat style -- kind of like the shortened version posted a ways above -- with elastic around the foot arch to hold it in place. Wear a short sock underneath.