While this is basically true for older LEDs that have a reverse breakdown voltage of several tens of volts, new high intensity LEDs can die from getting over 5V reverse. Say you have a LED that has a resistor for 12V and you connect it backwards, if it's a new LED it will problably die since the reverse breakdown current is normally about 5microamps. This information is in most LED data sheets, and i have killed a pair of LEDs this way myself too. Not all high intensity LEDs will die, however, some will. Just thought you should use that in the guide since more and more people use high intensity LEDs.
