You junky! ;0)
I was taking cans of Red Bull to work for a while. Then I noticed that far from making me feel better I was feeling strange and getting headaches when I 'didn't drink it! These things are properly addictive. They might seem to pick you up at the time, but on average you're a lot worse for drinking them.
Yes, energy drinks do make a difference, definitely. I tend to only use them if going for a ride that's a bit longer than normal. Lucazade is quite good value, although it's £6 for a tub it does quite a few litres. It a fraction of cost of the drinks you buy in sachets.
I think it was Jamie Oliver who said about kids drinking Red Bull that you'd be better giving your kids a line of coke!