Regrettably, the Wikipedia entry for "Citation needed" ("a common editorial remark on Wikipedia, which has become used to refer to Wikipedia in wider popular culture") doesn't include any actual assertions tagged with .
On July 4, 2007, the webcomic xkcd published a comic which depicted a protestor holding up a "citation needed" sign during a political speech.
In late 2010, banners with the template appeared at the somewhat tongue-in-cheek Rally to Restore Sanity and/or Fear, and in February 2011, at a more serious demonstration in Berlin against German defence minister Karl-Theodor zu Guttenberg, who had been embroiled in a scandal after it was discovered he had plagiarised portions of his doctoral thesis.
The New York Times has commented on the propensity of some "stickler editors" for adding the template to unattributed facts, and has used the phrase in an online headline.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.