There is a cool little app for iPhone, called The Perfect Egg Timer:
The perfect Egg timer iPhone application - AppStoreHQ
So you put the raw egg next to the phone to "measure" the size of the egg, put in your altitude, put in if it was in the fridge or room temperature, then put in how "runny" you want your egg. (See the screenshot in the link above). The app tells you exactly how long you should boil your egg to get what you want.
It pretty much works perfectly.
