I have been diagnosed as co-morbid ADD-Inattentive type (along with Nonverbal Learning Disorder, although the diagnostic criteria that some use to differentiate NLD from AS, namely, special interests and ritual behaviour, apply to me as well- but that's another discussion) and coffee tends to have the following effects on me:
After 1 large mug of strong coffee, I'm relaxed, less anxious, and could go to sleep more easily if I wanted to.
After 2 mugs, I am alert and better able to focus on projects and conversations.
After 3 mugs, I'm scary happy, and avoid people who aren't as wired, lest I disturb them.
Now, after a big wooden mugful of iced toddy that has been cold-brewed from last night to mid-afternoon, I am in a state of bliss for the next 7 hours.
But I don't tend to have coffee everyday, because I'm picky about the quality. Living in the South of the U.S., I tend to drink iced tea religiously. When traveling to Ireland and Scotland a few years ago, that was one of the few home comforts I found myself missing, in spite of the fact that they do hot tea much better.