The problem with blog footnotes
Here is something that has just occurred to me (courtesy of seeing an example of it): footnotes are hard to do well in blogs, and may need actual software support if you want them to be completely correct.
The conventional way of doing footnotes in HTML is to use fragment URLs and anchors, with the footnote text at the bottom of the entry and your choice of footnote markers in the main text. But, like anything involving anchors, this means that you need to come up with unique anchor names.
On one level this is no problem; you can just use 'fn:1', 'fn:2', and so on. But on another level this is a problem for blogs, because blog entries are repeatedly aggregated together with each other on web pages. When you put multiple footnote-using entries on the same HTML page, you need all of their anchors to be unique; you are not likely to get this if you use 'fn:1' style anchors. (This is especially pernicious once you start considering syndication feeds and 'planets', that put content from multiple blogs on the same HTML page.)
You can just punt on the issue and say 'well, it's up to the author to come up with unique anchor text (ideally globally unique text)', but in practice people won't always do this and this is equivalent to having non-functional footnote links under some circumstances.
Admittedly, I suspect that most people won't really care about all of this, and will be perfectly happy using 'fn:1' style links and having them not work. Regardless of whether the actual links work, your intent is likely to be pretty easy for users to follow.
(And who knows, maybe the proper implementation of footnotes in blog entries is pop-up alt text, like xkcd famously does on the comics images. Alternately, footnotes are a printed thing that are not appropriate in HTML.)