For awhile it seemed as though Pirates 4 was going to be shoved aside in favor of The Lone Ranger. But that proved to be idle rumor (or hopeful, depending on whether you prefer Tonto to Sparrow), and they decided to go with the tried and unsteady Captain Jack instead. It's believed he'll be chasing the Fountain of Youth this time, as indicated by the sequel grab in At World's End, and they've optioned Tim Powers' novel to give them an idea or two.
Of course, it's only January. A lot can happen between now and summertime, especially to a fourth installment of a franchise, and particularly when the third installment wasn't very enjoyable. Perhaps Disney and Marshall will be unable to decide on a villain, or the budget will skyrocket higher than the studio likes. With all this talk of angst and Twilight, will the teens and tweens still spend their money on a drunk pirate, even if he wears eyeliner? Come March, we could have a Pirates of the Caribbean reboot that'll focus on Jack Sparrow's teen years and his struggle to find his sea legs. All bets are off with these things, especially if there's a spin-off series just ripe for adaptation.