well this question seems to be quite old now but there is another very important reason why you should start with cold water when cooking related to the physical and chemical properties of water that did not appear to make it into any of the other answers.

The answer is related to the reason that warm pop gets flat. Compared with warm water, cold water's ability to store dissolved gases is superior. Warm water on the other hand tends to expel dissolved gases (hence the reason cold pop stays fizzy longer than warm pop). The reason you want to keep pop cold is to keep in all the CO2, but there are other gases dissolved in water that you generally want too, like oxygen gas (O2).

Hot water has probably been sitting in the plumbing system for some time, so a great deal of the oxygen gas has probably been expelled. On the other hand, cold water from the taps is more "fresh" and enriched with oxygen gas. Even after boiling water, the trapped gases will take some time before they escape. So if you start with cold water, whatever you're cooking with the water will become more enriched with oxygen gas than if you started with warm water.