Dany gets to hang around Slaver's Bay for a while longer.
Further information was not officially announced. However, based on comments by showrunners and other personnel, we know that Season 4 will again comprise 10 episodes and will largely be based on the latter parts of A Storm of Swords. It is unclear how much material will also be drawn from A Feast for Crows and A Dance of Dragons (the fourth and fifth novels take place concurrently, both overlapping with the end of the third novel). The climax of Season 3 appears to be an event that actually happens two-thirds of the way through Swords, and there are sections of the fourth novel which chronologically take place during the latter part of the third. Showrunners David Benioff and D.B. Weiss are certain to return, having signed a two-year contract before beginning work on the third season, and it is anticipated that George R.R. Martin will again be scripting one episode.
One tidbit that is known about the fourth season is that it will feature a battle that will dwarf the Battle of the Blackwater at the end of the second, and the producers are anticipating interesting discussions with HBO on how they film it. My personal view is that they should definitely call back Neil Marshall, who gave them a lot of bang for their buck with Blackwater.
Whilst we don't know what characters from the books will be brought into the show, fans are confidently expecting the casting of (at the very least) Prince Oberyn Martell and Lord Mace Tyrell. New locations to appear in Season 4 will likely include the city of Meereen.
Other recent info that has come out about the show indicates it is now HBO's most profitable series, also selling more DVDs and Blu-Rays than any of their other series. Sales of Thrones merchandise also make up more than 75% of all merchandising sales for HBO. With figures such as this (and the fact that Thrones allegedly makes more than 50% of its budget back immediately through foreign rights sales alone), HBO's decision is unsurprising. Indeed, some industry-watchers were even predicting a two-season renewal notice, allowing the producers to more efficiently segue from one season into the next, but HBO elected not to do this, at least not this year.
Thrones was also a ratings success for Sky Atlantic in the UK, hitting 600,000 viewers, a substantial increase over Season 2 (400,000) but not up to the highs of the first season (700,000).