Twitter previews official analytics service, prepares to release it for free
Mashable has two screenshots, one showing a "timeline activity" page, with your follows and unfollows over time, and then a list of your recent tweets, along with the number of favorites, retweets and replies each one received.
The second shot is a stats display for Promoted Tweets, one of the ways to buy ads on Twitter. Promoted Tweets has its own tab, where users can see how many clicks, replies and retweets their promotions are bringing in. This is probably the real reason behind Twitter analytics. Sure, the average user might want stats, but Twitter is making these stats free to all. The way this product makes money is by making Twitter's ad platform easier to use and more attractive to companies.
As for when Twitter Analytics might roll out to your account, it probably won't be this month -- the screenshots came from a Promoted Tweets user, so that group will probably get to test the service first. Twitter has said in the past that they're aiming to release Analytics by the end of the year, though, so it's likely you could be using it as early as December.