Some things to consider
Studies relating performance to caffeine

cycling performance tips

Seems like in order to see appreciable gains because of caffeine use, you need to intake a decent amount (180mg?) and at that point you start really seeing its diuretic properties. I know I've read somewhere that the diuretic properties are lessened during periods of increased activity, but having to hop off your bike for a pit stop is no fun...

For my personal experience, I like redbull or rockstar juiced before a ride, but it's by no means necessary. I don't know that I see that much of an enhancement other than a general increase in alertness.
oh, and I can't do coffee- it makes me have to pee too much, too often. Not fun when trying to do a long ride/stay properly hydrated. For some reason, caffeine pills, redbull and rockstar don't have this effect on me. hmm.