This is a very small update, but shows how Facebook is trying to make itself a more central part of people’s lives. You can now log in to the site by entering your username and password instead of your email address and password like before.
Sure, many other sites let you do this. But the more interesting part is that Facebook has been promoting usernames for months, having let people get usernames in vanity URLs earlier this year. For example, my personal profile is now at www.facebook.com/EricEldon. Now, I can log in as EricEldon. The significance, or what there is of it, is that Facebook wants you thinking about using the site on its terms, rather than, say, in terms of the Gmail or Yahoo account you’ve been logging in through in the past.
source: insidefacebook.com