In HTML or XHTML, there’s no such thing as a footnote. No structure for it exists at all. A fact like this is very difficult to get across, I find – a cochair of the WCAG Working Group required four separate explanations, for example. I think it would be pointless for me to try to persuade the more severe standardistas of the Tantek and Hickson ilk of the need for such an element; they’ll just laugh, as Tantek did when I asked about elements useful to newspapers. (But programmers will probably get blockcode. We know who really matters.) A markup language invented to present physics papers online was deficient for that purpose in the first place and will never be fixed.
Thus, David Foster Wallace cannot be adequately represented in HTML and Gruber’s footnotes aren’t footnotes at all, but merely a “Back to Top of Page” link in sequined cocktail dress and rouge. Hence they should not be given any more attention than such links have been. There’s no innovation whatsoever here, and even his choice of Unicode arrow character is wrong (we are not hooking and moving leftwards; we’re going straight up ↑).
Sorry for not being impressed, kids. This is an example of heaping praise upon an A-lister for doing something everyday and common under the guise of innovation. Give it a rest, please.