Drew Magary (404’d, sadly) (language is slightly salty):

Listen, asshole. If you think I should read something, just put it in the fucking text. [1] Any time I see a little superscript number above a sentence in the middle of paragraph I want to go find a Labrador and run it over. And any time I see multiple footnote citations in a single paragraph, I wipe my dick across the monitor. [2] And God help you [3] if you do it midsentence. I’m already reading your shit, asshole. Don’t go pissing me off by tossing little miniature bonus reading assignments in there in 8-point font. You are pushing your luck.

Because I know why you’re doing it. You think you’re so clever, so erudite, that you just HAVE to interrupt your story with a little EXTRA story or thought that shows off all the zany things you know. OOH! OOH! OOH, LOOGIT ME! I KNOW OF ONE OTHER FACT THAT ISN’T WHOLLY RELATIVE OT THE TEXT, BUT I’LL JUST DIE IF I DON’T SHARE IT WITH YOU!

Especially on the web, I don’t see a lot of compelling uses of footnotes. 99% of the time they’re a crutch for people who can’t rewrite a sentence to fit in a link or a joke, so they punish their readers by forcing them to stop and scroll all over the page.

Stop it. If you’re not a clever enough writer to sprinkle your little aside into a paragraph, skip it. Please.