Works as described; simple and elegant; needs CSS added, though

Well done, in spite of Covi’s comments from December of 2012.

I like that this works well with WP Post to PDF, too (including my own hacks to that plugin). The minor nit with the pdf output is that the separator line seems to be getting lost, but I’ll look into that.

CSS additions were a must for me. This could be an issue for more basic users who don’t fiddle with theme code or CSS at all. I’m using a child theme, so this was relatively simple. I tweaked John’s “suggested” CSS a bit, too:

[...]
sup.footnote a {
  text-decoration: underline;
  vertical-align: super;
  font-weight: bold;
  font-size: 80%;
}
[...]

(I wanted to make the footnote number stand out a bit more, and make it look more like a link.)

Bravo, John. Nice work. A few $$ to follow.