The site dominates the U.S. market for classified advertisements, with nearly 27 million unique monthly visitors (Ebay’s Kijiji, by contrast, has just 2.3 million U.S. visitors/month). But the fact that the service was available only in English hurt it internationally, where Kijiji is a close second.
Craigslist is now available in Italian, French, Portuguese and German. “Basque, maybe Klingon” are coming soon. :-)