In addition to real-time Tweets about the weather, Twitter today brings another feature a "profile mention box".
The feature places a Tweet box on users' profile pages so you can direct Tweets at them right from those pages without having to jump back to the main Twitter.com page or reply to a specific Tweet that user sent.
The box features grayed-out text that reads: "Tweet to @USERNAME". When you click in the box, that text is replaced by a pre-populated @USERNAME intro, after which you type to that user.
This is a bit like Facebook message wall on profile pages, prompting users to send public tweets (a.k.a @ replies, or mentions) to specific users directly from their profile pages. Of course, unlike a Facebook Wall, your Tweet won't appear on another users' profile page, it will simply go into the main Tweet stream.
The feature addresses a problem among new users: namely, that many of Twitter's functions are not intuitive. New users must learn, either through guides or by observing other users, how to send replies and direct messages.
The screenshot below is from mashabel who reported this month back.