I'm sorta on the fence with this one now. Since I run an all alloy motor, I run anti freeze for it's corrosion inhibiting properties but I'm sure it's a non ethyl glycol based type, that stuff hard to get over here. I'm not even sure if it hasn't been banned from sale.
All you guys running iron blocks and aluminium heads have a v8 battery, I'm not sure you'll be best off running de-ionised and/or de-gassed water? Don't use R-O water thats the worst thing you can do, I've worked on renal dialysis machines and that stuff eats steel and aluminium at an alarming rate. The purer the water the more corrosive it is.
HTH's