I recently bought a Veskimo water-cooled vest and have been trying it out in the heat lately. Yesterday (Saturday) was the real torture test. The ambient air temp was 102F and with the humidity it felt like 115F (reported by the XM radio). The Vision temp gauge varied between 104 and 107 at all times. The Veskimo works as advertised and kept my body core cool with the 65F water constantly circulating. The warmest part of me was the brow line in my helmet which had a small bead of sweat, but for the most part, I was dry and comfortable. I rode for 1 1/2 hours and had about 1/2 the ice left when I returned home - so it would easily go as far as my gas allows before needing new ice from a gas station or 7-11, even in 100F+ temps all day. I must say, it's been worth the money so far. Some have suggested that the vest is simply over the top - take a car. I say if you ride with a heated vest for cold, this is not much different and is really simple to setup once you know how. It takes all of an extra 5 minutes and sits easily in the seat behind me. I guarantee I wouldn't have been out for leisure riding yesterday without it.

I almost grabbed the camera for some pics of me in full AGATT in the sun on a 107F degree day. And, that's another benefit: using the Veskimo, I am not only cool to ride, but ride in full protective gear while the guys/gals in shorts and T-shirts are dangerously exposed to sun and gravel. I'm a believer.  Here's a photo of the system I have, with the 9 qt container for the back seat (or rack, etc). 

And here's an image of someone else wearing the gear with the cooler behind.