Eggs should actually only be boiled for a very short period of time and then simmered until the white and yolk are cooked just how you like them.
I find that the best way to "boil" an egg is to gently place eggs into a rapidly boiling pan of water and immediately lower the temperature of the water to around 180°F ( just over 80°C ) so that only the occasional bubble is rising from the bottom of the pan. Starting the eggs in boiling water makes the shells easier to seperate from the eggs when you are peeling them but the temperature must be reduced to ensure you don't end up with rubbery over cooked eggs which start to smell faintly rotten.
If you wan't to cook the perfect "boiled" egg I would recommend getting yourself an instant thermometer so you can measure the water temperature accurately and a reliable kitchen timer so you can ensure your eggs are cooked for the required duration.
How long should the eggs be simmered for ?
The answer is it depends on the size of the egg and how you like them cooked.
For soft boiled eggs with cooked whites and runny yolks remove them from the simmering water after around 4 - 6 minutes.
For medium eggs with a partially cooked yolks the eggs should be left to simmer for around 6 - 8 minutes.
And for hard "boiled" eggs they should be left to simmer for 11 - 13 minutes.
Cooling hard boiled eggs.
If you plan to use your hard boiled eggs in cold dishes such as salads or deviled eggs you should take them straight from the simmering pan and place them into iced water for at least 15 minutes, allowing them to cool completely prior to peeling.