Yup, and not a 2D conversion either. Here's the story from Coming Soon:
A lot of the 2011 summer tentpole releases have already been announced as being either filmed in 3D or converted afterwards, but so far, May 2011 has been somewhat devoid of 3D release announcements... until now!
Walt Disney Pictures has announced that the fourth installment of Jerry Bruckheimer's popular action franchise Pirates of the Caribbean: On Stranger Tides, directed by Rob Marshall, will be filmed in Disney Digital 3D. Bruckheimer's only previous 3D movie before that was last year's G-Force.
Pirates of the Caribbean: On Stranger Tides is still slated for release on May 20, 2011.
-Least it's not a conversion, though I'm not a fan of the franchise...thoughts?