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.  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.  And God help you  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.