Yahoo! Mail now providing a reply bar that appears at the bottom of your email messages and lets you quickly reply to messages from your friends and social network.
If you get a lot of Facebook and Yahoo Groups email notifications about activity happening in my social network. Now, you can simply click into the reply bar at the bottom of my message, type my message, click send and you're done. Now on to my next message. It's simple and fast.
[Source: Yahoo Mail blog]