Facebook is quietly making the default email address in your contact info your Facebook.com address. Seems sneaky, but it’s a good thing. Probably. You might not know this, but you have a Facebook email address. It’s [yourusername]@facebook.com. The thing about it is that it unifies SMS messages, instant messages and emails in a single system: The Facebook Message.
… The official explanation for the change, according to a Facebook spokesperson, is this: “As we announced back in April, we’ve been updating addresses on Facebook to make them consistent across our site. In addition to everyone receiving an address, we’re also rolling out a new setting that gives people the choice to decide which addresses they want to show on their timelines. Ever since the launch of timeline, people have had the ability to control what posts they want to show or hide on their own timelines, and today we’re extending that to other information they post, starting with the Facebook address.”