Does anyone know if there any negative effects of drinking red bull or similar energy drinks regularly?

I typically use tea (caffeine) as my stimulant of choice on a day to day basis, but the effects aren't that large. During large Magic: the Gathering tournaments, I typically drink a red bull or two (depending on how deep into the tournament I go) in order stay energetic and focused - usually pretty important/helpful since working on around 4 hours of sleep is the norm for these things.

Red bull works so well that I'm considering promoting it to semi-daily use, but I'd like to know exactly what I'm buying if I do this.

Edit: After saying it out loud, I just realized that if I use red bull regularly, it might lose its effects due to caffeine/whatever dependency. TNSTAAFL strikes again :-/ Still interested in any evidence though.