Facebook created a system where users were able
to create usernames for their profiles, so instead of a long number in
their domain, a name like jsmith would appear. Facebook also had rolled
out an email service
for its users who would have a name@facebook.com and could communicate
with other users of Facebook or even other services like Gmail, Yahoo!
and Hotmail. Because the two services were launched at different times,
users may not have created a username for their Facebook profile, while
they did for email (and vice versa). Now, according to Mashable,
Facebook is rolling out a program where the two usernames of both
services will be synced (unless you have already chosen different
usernames for both services, those will remain unaffected).