I know you have been waiting for this feature since long now and the title made you understand all. Yeah, you are correct now you can login into facebook.com using your username in place of your email address.
This announcement was declared on the facebook blog few days back. After introducing fconnect and enabling the facebook users to login into any 3rd party websites, facebook has made the things go more simpler. It has allowed all of its users to login using their facebook usernames. 
This was missing when the username feature was introduced by facebook earlier this year. So next time when you login into facebook you put your username instead of putting your long email . It also avoids you to put your email address on the public machines.
It is worth noticing that the period ( . ) in your facebook username holds not much significance in your username. This means if your username is user.name, then you can user any of the username or user.name to login into facebook account. Hope that saves your another keypress.
Facebook is integrating features slowly gradually to become a big, robust application. I am sure you are enjoying it as much as the facebook team is enjoying it by releasing these cool features.
Stay Digified !!
Sachin Khosla
