Facebook Usernames
Via @mullican: Facebook will soon let you choose a unique username to represent your Facebook account. More details on Facebook’s blog.
What Does This Mean?
How is this different from the way Facebook currently works? First, your username will be unique — many people are called John Smith, but there can be only one ‘johnsmith’. Second, Facebook will begin using usernames in profile URLs (probably inspired by Twitter):

Facebook also say that they “expect to offer even more ways to use your Facebook username in the future”.
Should I Care?
It depends. If you’re a casual Facebook user, this probably doesn’t matter. But if your online identity is important for you, it makes sense to claim a Facebook username that matches, or is close to, the usernames which you use on other services.
Facebook will be allocating usernames on a first come, first served basis, starting (unfortunately) at 5 am on Saturday 13th June. So if you’d like to get a Facebook username to match the one you use on Twitter, set your alarm clock, and bookmark this page.
PS: if your name is James Wilding, forget you read this may the best man win.