A couple points from How Coffee Can Energize Your Workout gives these refreshing points for the coffee lover:
Go by the clock (and calendar). If coffee is programmed into your exercise schedule, drinking it 30 to 60 minutes before you start will put your blood level of caffeine at a peak during your workout. If you are a coffee regular and a big event is coming, like a marathon or 100-mile bike race, [Nicholas] Gant [director of the Exercise Nutrition and Metabolism Laboratory at the University of Auckland in New Zealand] recommends that you gradually taper down the week before, so that a modest amount the day of competition will get you going.
Don’t sweat dehydration. Too much coffee and your body will suffer because caffeine is a diuretic and make you lose vital fluid—or so goes the belief. It’s not true, says [Leslie] Bonci, [registered dietician and director of sports nutrition at the UPMC Center for Sports Medicine in Pittsburgh]. “It’s a common misconception that when you consume caffeine sometimes you feel the urge to void,” she says. “But in studies that looked at the urine volume produced over 24 hours whether or not someone consumed caffeine, there’s not a significant difference.” The problem with the misconception is that it leads many a coffee drinker to compensate by drinking much more water than necessary, and that could send any jogger running for the nearest bush.