I had two typos on the original note I wrote that I just corrected.
I was off just a little on the number of flights that Delta has in Atlanta. Last summer it was 1038, as per this article in Travel Skills. It is a great article, and gives a good insight on how Delta operates, especially in Atlanta. I would assume that there will be around 1050 flights this summer.
http://travelskills.com/2014/07/01/behind-scenes-delta/As the above poster said, VS will have no problem being extremely successful with their Atlanta flights.
As for the poster(s) who are worried about connection times, that happens with any hub operation. Just give yourself plenty of connection time (if you can), and you will be OK. Atlanta has the train system that can get you all over the airport pretty darn fast.
As I stated before, I have been using the airport for 27 years. I know it backwards and forwards. But with any airport, it can have its problems at times, (like summer afternoon thunderstorms), but it does recover pretty fast.
For the posters who were mentioning/asking how busy LHR is, here is a link to the busiest airports in the world for 2014. In 2014 Atlanta was number 1, Beijing was number two, and LHR was number 3.
http://www.cnn.com/2015/03/26/travel/fe ... port-2014/