Don't run with pure water for too long. The additive isn't just to stop freesing it also prevents corrosion of the metal surfaces of the cooling system and possible the build up of limescale and sludge. I know of people who have radiator failures after running with low additive; Also one case where an aluminium stub that a hose connected to becoming corroded and snapping off, leaking out all the coolant.
A question for you though: do you guys routinely use distilled water for your coolant mix? This sounds like a good idea. In the UK a lot of people use straight tap water.
You heard the man tubbs - get undressed.
I've been meaning to change mine- I have 178,000 on my '94 SE-R and I've never even had the radiator cap off. It's never run hot or anything, and I've lived in Raleigh (hot) and Maine (extreme cold). Go figure.
Well down here in Miami it is very hot and humid so coolant flushes should happen about every year. It is also good to flush the system so you don't start rusting from the inside out. I use a 70% water to 30% coolant mix and 20 caps full of water wetter and my temperature never moves a bit even after several hard races.