If you use Twitter's webapp, you'll be used to seeing notifications that you have new interactions in the top bar. Soon, you'll see those pop up directly in your timeline.
The new interface will show you when someone retweets or replies to one of your tweets, and will allow you to reply to that reply directly from the notification. If you'd prefer not to be bombarded in that way, you can switch off notifications for retweets, replies, when a tweet is marked as a "favorite", new followers or direct messages.
As with most changes on Twitter, this is being rolled out gradually, so it might be a few weeks before you see it.
Stay connected with notifications on twitter.com [Twitter Blog]