Ordered this bag for a week long back country trip were temperatures dropped into the low 20s, and woke up to open the bag for ventilation each night. This is my new favorite bag, though too hot for any summer trips. Note the neck collar has a learning curve with the set of velcro patches and pull strings; once you figure out that system (not that complicated once you try it out) it's actually very efficient and keeping heat trapped in the bag.
Final note: keep an eye on shipping if you order 2-day. It took mine a week to arrive after lots of back and forth with campsaver (there representatives were helpful, at least).
This review was written in the old system and had content requirements that are different than reviews written today.