I love - I mean LOVE - my Jetboil. Simple, light, convenient... It is everything that my Whisperlight International is not.
I love the way it packs, I love its quick boil times, and how many boils it squeezes out of one cannister. (I recently completed a Northville Placid thru hike with a partner and one cannister lasted us all the way to the last day). It is the perfect piece of gear for the solo hiker (or small group) who does not care about gourmet meals. I personally just boil water for my meals... no simmering and certainly no frying or anything like that.
BUT - here is the rub. I took it out over Thanksgiving weekend and the performance was shaky. Boil times were significantly increased to more than double that of warmer weather times - and this was at temps in the high teens to 20's and 30's. Cold and below freezing but nothing outrageous. In addition, after a night out there, a cannister with about 1/4 of the fuel used simply refused to start. Upon replacing it with a new cannister, the stove sputtered noticeable on start, flamed out, then started again. Now, I didnt take any precautions with these cannisters. I didnt warm them, or baby them in anyway. They were stuffed in my pack, not carried close to my body. But still, at that temp, I expected better performance.
This is not my final go at using the Jetboil in cold temps, I'm gonna try to find ways to improve its performance - but based on my first winter trip, this looks to be a 3 season stove.
I've always heard that cannisters are poor performers in colder temps, yet most mountaineering books I read (including some of Joe Simpson's classics) always reference using cannisters on their expeditions. Whats the deal with that?