Um, the whole point of the blood system is to overcome the squared area vs cubed volume problem. So you can cool larger things fast if you use blood vessels to move fluid that carries out heat.
Kinda.
If you circulate a coolant through the circulatory system, the cooling speed is limited by the coolant heat capacity and mass flow rate. For a given maximum pressure difference, the maximum flow that you can achieve depends on the fluid density, viscosity, and the structure of the circulatory system. In the simplified case of laminar flow through a stiff circular straight pipe Hagen–Poiseuille equation applies: mass flow rate is proportional to fluid density and the square of cross-sectional area, and inversely proportional to fluid viscosity and pip...
http://www.strike-the-root.com/51/walker/walker12.html
Came across it pretty randomly, I found it quite intriguing. Cryonics is "routine" for human embryos, not far-fetched for humans at all. Makes the whole thing seem potentially very reasonable (and me someone who hasn't signed up and doesn't plan to).