According to a report from Search Engine Watch, citing numbers from comScore, Yandex is now bigger than Bing in terms of worldwide monthly search queries.
Search Engine Watch's Michael Bonfils says Microsoft sites processed 4.477 billion queries while Yandex processed 4.844 billion in November and December. That would make Microsoft (and Bing) number five. The top three are Google, Baidu and Yahoo.
Last month, Yandex seemed poised to make a mark here in the U.S. (or at least attempt it), but the company's plans were spoiled by Facebook. Yandex launched an app called Wonder, which was a new take on social search and relied heavily on Facebook data. Facebook deemed it a competitor (particularly since it had just launched its own social search offering in Graph Search), and cut the app off. It's against Facebook's terms to use Facebook's data in a competing service.
Facebook's Graph Search could, however, actually help Bing if it gains traction. Bing provides the web results, which are the default when Facebook doesn't have the appropriate data for a query. Graph Search is still in early beta, and is still slowly rolling out to users.