Second round applicants were notified in early March of their status. Applicants who were offered spots were telephoned the first week of March (and sent an acceptance packet), while those who were not were notified about a week later.
The preferred deadline for response was April 15th, so next year's class should be filling out.
CBParent, out of curiousity, who is your son? I was invited to attend DS, but chose not to in order to attend Duke as a Robertson scholar. The decision was the hardest I've ever made, so I understand the difficulty your son might be having in choosing.