I hiked the AT in 2004 & 2005. In 2004, I a HH Hennessy Explorer Ultralite A-Sym & used a 3lb air mat. It was like making love to a large whale. (I'm guessing on that) I got a JRB Nest toward the end of my hike and loved it. The coldest it got at that time was in Maine at @ 18°F
In 2005, I used both the Nest and a 16 oz 3/4 Therma Pro lite until it warmed up and then I ditched the pad.
I also had a JRB Weather Shield - Under Hammock, which added several degrees plus protected the Nest from rain, and blocked the wind.
I plan to hike it again in 2014 and I'm not sure what my setup might be. I now also have a 20°F Phoenix from www.hammockgear.com