My son did not receive any email notification for NASS last year. He applied on Feb. 1st and received an acceptance letter in the first week of April.
I started reading these forums just over a year ago and it seemed that only a few people reported receiving letters in March, and a lot more received their letters in April. My son had a strong application, but we live in a competitive area of Georgia - you never know what may help/hinder you getting accepted to Summer Seminar and there is nothing you can do about your geographic location. Remember that Summer Seminar is largely a recruiting tool (geographic, diversity, etc.) and as has been repeated numerous times on these boards ... many people do not get into Summer Seminar, but go on to get an appointment. Do not give up if you don't get accepted for NASS!
Good luck with the waiting! Remember that the recent bad weather has put the Admissions Board a bit behind (a BGO reported that they were now meeting twice a week just to try and review all the 2014 applications by April 15th
http://www.serviceacademyforums.com/showthread.php?t=10891 ) and so it won't be surprising if the Summer Seminar acceptances are also a bit delayed this year.