I have taken 200mg of Modafinil daily for more than 5 years.
Before it, I could go to sleep just about anywhere and just about any time. I could easily sleep for 12 to 14 hours a day if I let myself. When I had a work commute of about an hour and a half, I would have to pull over, sometimes four or five times, during the afternoon drive home to take cat naps because I couldn't keep my eyes open. It didn't matter how much or how little coffee I drank, it didn't matter how much I slept the day before, and it didn't matter whether I was eating my typical diet which was fairly healthy, or if I had unusual amounts of junk food that week.
Caffeine doesn't work "normally" for me. I like the taste of coffee, I usually have one cup a day that I sip throughout the morning. However, I don't have a Folgers moment. I am not groggy until I get my first cup. If I drink a soda or coffee or even have a shot of espresso in the afternoon, I don't get a sudden boost of energy. I don't even get the boost of energy from energy drinks. When I drink a lot caffeine or other energy drinks in a short period of time, I find that they will give me a mild case of the jitters, but even then, they don't counteract my actual drowsiness. Hence, I've never gone higher than my typical cup of coffee in the morning and frequently a soda in the afternoon. More than that has almost all down-sides and no up-sides for me.
I took a sleep study, and I was not diagnosed with narcolepsy because that diagnosis is very specific. You must immediately fall into REM sleep. I was diagnosed with a "we have no idea what you have" condition of excessive daytime drowsiness and received a prescription for Provigil. Originally, it was a 100mg dose, but when that was not effective, it went up to 200mg.
It is a bit of a wonder drug for me, but certainly not in the terms that it was described in this article. It doesn't make me hyper focused or give me unusually sharp focus, it just removes the incapacitating drowsiness I suffered in the afternoon. I've actually found that music is more distracting to me during work hours since I started taking it. While I still enjoy listening to various types of music for recreation, I don't play music while working anymore.
I would definitely say it is not addicting in the manner that coffee is. On vacations and at times I didn't have my prescription with me, I've gone weeks without taking it. There are no withdrawal symptoms, other than the fact that I would be excessively drowsy again, especially in the afternoon. If I stop drinking caffeine, I will suffer migraines for about two weeks.
I will agree with the part about broad focus vs narrow focus. I can think better about large system design late in the evening. When I am working on an architecture problem during the afternoon, I find myself frequently rat-holing. I'll focus on one specific part and just keep going back to it over and over rather than spending enough time at the higher level.