Quite a few people have reported receiving appointments on the collegeconfidential.com discussion boards. My son also has not heard anything.
This is total speculation based on how I would go about the appointment process so take it as nothing more than that but my guess is that, after March 1, the review board identifies the top candidate from each remaining congressional district, makes an offer, then goes through and makes offers for all the at large slots to the highest whole person scorers of the rest, and if the acceptance rate is lower than expected, makes offers to the highest whole person scorers of the remaining. If the process is as I described, I have to believe they are well into matching up the at large candidates to available slots.
The website indicates most should know by April 15 and if I understand the process correctly, there's a courtesy week built in to the notification process to let MOCs notify candidates and then another week built in to mail and have the candidate take receipt of the appointment, so it seems like we would be getting close end of the main selection process.
Again I'll state my disclaimer. That's total speculation. I work in systems development and so I tend to over think these types of things.