The central message behind the commandment against hot drinks is this:
Habit-forming substances are to be avoided.
To preserve the integrity of the spirit, the body (in which the spirit dwells, during mortality) must not be reliant on psychoactive substances. Reliance on these substances can impede one's ability to communicate with God.
It is said that the Holy Ghost accompanies us on a daily basis as long as we live according to the Word of Wisdom. But the highs and lows that come along with stimulants can push the Holy Ghost away.
Energy Drinks: The Lift That Lets You Down
Caffeine—The Subtle Addiction
Given the withdrawal symptoms that regular caffeine consumers suffer when they abstain from caffeine (fatigue, headache,) it's clear that caffeine is a habit-forming substance. Therefore, it should be avoided.
This is not an official position of the church, but the above articles give some idea of what LDS writers think about caffeine.
Originally drafted as an answer to this closed question about caffeine.