erm, I think you should re-read the link that someone has already posted to the AIS site.
"small to moderate doses of caffeine have minor effects on urine losses or the overall hydration in people who are habitual caffeine users. In addition, caffeine-containing drinks such as tea, coffee and cola drinks provide a significant source of fluid in the everyday diets of many people."
And the second part of your statement doesn't make a lot of sense. If the high was "slow-release" then doesn't that mean you would feel it for longer?
And regarding the laxative effect that others have mentioned - thankfully my body's pretty well trained now so when there's a race on, I generally pay a visit to the dunny just as I start to put bike clothes on pre-race.
Chris