Virginia Heffernan in the New York Times Magazine:
With more than four million definitions submitted so far, and 2,000 more coming in every day, Urban Dictionary is a stunningly useful document that unlike most media is made and used by actual young people — in droves. The site had 15 million unique visitors in April. In a typical month, 80 percent of its users are younger than 25. The population with the biggest ego stake in slang — divining it, protecting it, practicing it, spreading it, declaring it over — actually creates and patrols the content.
Almost perversely, Urban Dictionary avoids most of the standard dictionary apparatus. You won’t find information about parts of speech, etymologies or even standard spellings in it. Its sensibility, in fact, borders on the illiterate, which must be a first for a dictionary. It’s also packed with redundancies and made-up entries. This chaos seems to please Aaron Peckham, the company’s founder and chief executive. “Wikipedia strives for its N.P.O.V. — its neutral point of view,” he told me by phone. “We’re the opposite of that. Every single word on here is written by someone with a point of view, with a personal experience of the word in the entry.”
Better, then, to accept at the outset that Urban Dictionary is not a lexicographical project at all. Its wheelhouse is sociolinguistics.