I've tried Red Bull a few times, and to be honest I can't see what the fuss is all about since it doesn't seem to affect me in the slightest. Well, other than in emptying my wallet.
I think that people buy it and other similar products (Rockstar, Monster, Amp, etc.) based on the hype around it. Look at the adds promoting them, they depict it as a partygoers or active persons drink. In their adds they show pretty people having fun/doing cool things. People buy it based on the ignorant association that since cool people must drink, if they drink it, or more importantly, are SEEN drinking it, they will be cool/other people will think they are cool.
That must be the case because they are absolutely horrible for your body. Its only real use is a stimulant to alcohol.