We knew that Facebook had bigger plans for vanity URLs/usernames when it opened them up for registration this summer.

The popular bet was that it would create a mention/reply system similar to Twitter's @replies. That was shot down this week when Facebook launched its mentions system, which uses real names. But now Facebook has started letting users log in with their usernames.

More: http://news.cnet.com/8301-13515_3-10356274-26.html

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