Skipping the story book, I work rapidly changing shift-work and couldn't sleep, stay awake, or function when i was supposed to. I saw a specialist that diagnosed me with "shift-work disorder." The solution cocktail includes Ambien to go to sleep, and Modafinil/Provigil to stay awake. I only use them during the times when I'm on the odd-ball shifts (not days), and they work great. I've had no issues.
I have also recently gotten prescribed Adderall after voicing my (and former teachers) life-long concerns of possible ADHD. Low dosages did nothing, and I can "kind-of, maybe?" tell some improvements with a higher IR dose. I don't want to ask for more at risk of looking like a drug seeker, and I don't want the jitters to increase, but I'm also not really sure what I'm supposed to "feel."
Until I've recently went back onto one of those odd-ball shifts and took modafinil again. I can absolutely without a doubt tell that I'm on it. I am focused and am constantly completing something. This is what I imagined Adderall was supposed to be. The con is that it has this effect that I don't notice I'm hyper-focused until many hours later when it wears down a bit, and it's noticed in retrospect. It's weird enough that I take it as rarely as possible (I'd rather feel this then constantly falling asleep while at work, which is extremely dangerous at my job)