Here is an example: half the internet (and at least one book on haircare) thinks that Erica Feldman or Ian Gutgold invented the hair straightener, based on schoolkid vandalism in Wikipedia 6 years ago.
It's listed in the list of Wikipedia hoaxes and is also one of the top 5 trolls listed on "House of Geekery".
It is back in Wikipedia right now:4) Erica Feldman
I imagine writer Li Mei Rong wasn’t taught in school that Wikipedia isn’t legitimate reference material, but she’d likely be well in the know now. In 2006, Erica Feldman and a classmate decided to place Erica’s name over Madam C. J.Walker’s as the inventor of the hair straightener. Originating on Wikipedia, it soon spread all over the internet, and into Li Mei Rong’s book, that Erica Feldman was in fact the inventor of the straightening iron. The hoax still lives on today, even after Wikipedia finally fixed it two and a half years later. Just Google Erica Feldman, or “Who invented the Hair Straightener?” and you’ll surely see the reach of this.
Of course, it cites a source: a website that copied it from Wikipedia. (The actual inventor of the hair straightener, before the Wikipedia vandalism, was Madam C J Walker.)
Wikipedia is spreading lies as well as knowledge. With 4 million articles, editors are stretched much too thinly to ensure quality control under the present set-up.
Also see previous discussion on Wikipedia Review.