Before when you typed @ and your friend's name into the Twitter text box and clicked on "update" all that happed was that you updated your site with @ and your friend's name. Now when you type @ and your friend's name into the Twitter text box, you'll be able to actually send a twit to your friend. If you wanted to reply to someone's post you had to do it from your phone or from your IM.

Even better is Twitter's new @Reply icon. After every post on your site, from your friends, you'll see a little swoosh icon. Click on that and the @Reply is instantly added to your text box. Then you can start replying to messages from your friends.

I love this feature so much. Replying to friends was difficult before, took thinking and work. I like to do things on the fly, I don't want to think about it too much, just do it. Now I can!