I've never had an energy drink and honestly I don't really feel the need to have one either. That said, obviously everything needs to be done in moderation.
I only ever consume this substance along with alcohol in clubs, to combat the drowsiness from beer - I find i have very peculiar hangovers if I have a few too many... I used to use them when I religiously bmx'd thinking it would give me more energy, but all it did was give me a 5 minute rush of energy and an hour long crash from having a complete lack of energy, waste of time!!
I used to drink 2-3 cans of Amp a day, but that was when I would have school from 7:00 to 3:00 then go straight to work afterwards and work 3:30 to 10:30 or 11:00. If I didn't drink some kind of energy drink I would be falling asleep at the wheel on deliveries.
I'll occasionally have one of the lucozade/gatorade/powerade flat "sports" types drinks, usually when playing sport. They've got electrolytes.