I grew up in PA, and have definitely camped below 0 degrees. It also gets quite a bit colder in the N. Georgia mountains than it does in Atlanta. I'm hoping for temps close to zero at the upcoming New Year's hammock hang on Springer Mountain in Georgia, and then the winter hang at Mount Rogers in VA, if I can make it. I've done sub-zero in a tent, but it will be first time pushing that low in my hammock. Ought to be tons of fun.
I'm dying to move out of Atlanta and go somewhere that gets real winters again. I want to go somewhere so cold I'm using snowshows and a pulk sled to do my hiking. THAT would be some quality time in the outdoors...