According to this article on Tek Goblin, the Concise Oxford English Dictionary (COED) has added 400 new words, among which my all-time favourite: woot. From the article:

To celebrate, the lexicon published its 12th edition today that adds more than 400 new entries -- many of which reflect the technological vocabulary found in today's society, like "woot," "mankini," and "jeggings."

The words are chosen by a small team at the Oxford University Press' academic cabinet which involves keying popular words into a database that shows frequency of use in print and online. Since publishing its first edition back in 1911, the COED shows how the effects of social media and instant-access technology on language has created a variety of new words while modifying existing definitions such as "follower".