I've been disappointed both in the neoprene socks and in Polar bottles. REI had Polar bottles on a clearance table last year and I bought two of them. After they didn't seem to work very well, I put a regular bottle, one with a sock and a Polar out in the sun for an hour, then stuck a thermometer in them. They started at 55 degrees (temp out of the tap from our well). and there was only 5 degrees difference top to bottom at the end of the time. It was detectable when I drank, but nowhere near enough to make me say, "Ahhh."
They both do keep water from freezing quickly in winter, but if it gets that cold, I usually don't ride long enough for that to happen anyway.