For an xkcd fanboy, you sure aren't putting any science or facts behind your claims. Randall would be ashamed.
Adderall is an amphetamine, lasts about 10 hours and is basically a controlled substance, banned by major competitive sports organizations as a performance enhancer. Caffeine lasts about five hours and (as far as I know) isn't banned anywhere. There's more sciencey ways to compare them but i'm lazy. Check the wikipedia pages.
Apparently not only can the caffeine make you more likely to be dehydrated, it takes between 45 mins and 1 hr to absorb fully into your blood stream. So really, if you want to try to use caffeine (or a caffeine-like substance like Guarana) make sure you take it about an hour before your workout for peak results. And i'll remind you all that continuous use of caffeine can make you dependent and dull the supposed benefits over time. And also, stay hydrated 24 hours before you work out; chugging a bottle of gatoraid while you run is not being hydrated.
(All that being said, I think it's a lame cheat to use a stimulant or performance enhancer when working out. Unless you're trying to win a marathon (which is still cheating) you don't need any "extra edge" provided by $2.50 sugar water. Do the reps and get sleep and eat good food and you'll benefit the most)
You don't need anything other than plain water for normal exercising (anything under 2 hours will generally count here). --Sports drinks will simply add calories and are not going to enhance your performance.
If you're going to be working out all day or doing something like a marathon, then you need to consider something to help replace the salts you lose when sweating.