bmike, Ive had an OR insulated jobee with the zippered top for well over 10 years, prob more, and use it mostly in a fanny pack when XC skiing. Works very well and Ive never had water freeze in it down to -20c or so, but then realistically the water in the 1l nalgene doesnt usually last that long anyway before being drunk, but it certainly is nice to have some warm stuff in there that will still be warm after an hour or two (I used to mix weak gatoraid from powder using hot water)

I do use it once in a while on a really hot summers riding day, in a pannier just to have some cooler water after the two bike bottles get finished. Prob is with dark coloured panniers that the sun warms them up so much it is surely hotter in there than on the bike frame, but in the end, having any kind of insulation is going to help a certain amount.