This thread's a little... old, but I'll ramble about ADD. I have a lot to say. You may find it interesting.
First off, to the people who say it doesn't exist: are you a doctor or licensed medical or psychiatric professional? No? THEN SHUT THE F%$# UP! Skepticism is one thing, but the opinion you hold is the exact opposite of what roughly 20 professional medical societies believe to be true, including pretty much every regulatory body in the US, Canada and UK.
Now, that being said, I think there's something to the skepticism. But more on that later.
Anyway, ADD is something I've been diagnosed with since I was in 7th grade. My parents were hesitant to even consider the possibility at first, but after coming across a few ADD kids and going, "why does that kid remind us so much of our son," they decided to give it a shot. I can tell you that right off the bat the medication helped, though interestingly enough I only know that from what OTHER people tell me. The initial round of medication was supposed to be a four-week, double-blind test. After two weeks my teachers all requested that the double-blind be stopped because, "from his behavior we all know which was the sugar pill and which wasn't." (And yes, they were accurate)
As far as my symptoms, I have most of the usual ones: easily distracted, appears not to be listening (though I usually am), poor to no grasp of subtlety, excessive speech, forgetfulness, procrastination, interrupting others, and I'm ludicrously disorganized. The symptoms are drastically minimized (though not eliminated) by the medication, save for the grasp on subtle social cues. (Watch me try picking up a girl sometime; it's different. It works, but it's different) Interestingly enough, there's another symptom I have which I hear very little of; one of the few things I noticed when I first started taking medication was that I would get a feeling of relief and happiness when I completed schoolwork. I never got that before I took medication. I had no idea you're supposed to feel anything after finishing a job, other than slightly less annoyed now that whatever it was isn't taking away valuable video game time.
To this day I'm still taking Ritalin for ADD, but usually all I need is one pill in the morning and I'm (relatively) normal for the rest of the day. It is very obvious to everyone around me (but not me) when I am or am not on my medication. It's obviously doing something. I certainly know I couldn't function as well without it, or at least without some form of treatment. (Pills are just a lot easier and effective)
Now to the skeptics (again) I do think there's something to the skepticism over the disease, particularly how it's "just an easy fix for bad parenting." I actually kind of agree with that sentiment, but in a limited sense. See, there's a lot of difficulty with diagnosing ADD; there are no medically verifiable symptoms, just psychological ones. Hell, they don't even know what exactly causes it. (Though my personal opinion is that what we know as ADD is really anywhere from 6 to 20 different diseases which have markedly similar symptoms) One of the key symptoms of ADD, but not criteria for diagnosis due to the nature of it, is fragmenting internal thought patterns. Here's an experiment: try asking a kid how they think, and if its fragmented. You probably aren't going to get a good, reliable or even consistent answer. On top of that, there are dozens of other things that can cause textbook ADD symptoms: high sensitivity to caffiene, hyperthyroidism, even a simple protein deficiency can cause ADD symptoms. Since diagnosing ADD is basically done by identifying symptoms and then eliminating all known "testable" causes this can lead to TONS of misdiagnosises. So many of these possible "ADD imitators" are fairly obscure, usually only known to specialists in a particular field, NOT by General Practitioners or anyone who's likely to be doing the diagnosing. Even if they've specialized in ADD and read up on alternate causes for the symptoms more than likely they'll have missed one or two really obscure ones.
I've had second-hand experience with misdiagnosis of ADD. My little brother was diagnosed as ADD, but no matter what medication or treatment he tried it didn't help very effectively, or at all. Several months after the diagnosis he went in for an unrelated problem and the matter of his low protein intake was brought up. He'd had protein deficiencies off and on all his life, what with being a vegetarian and a picky one at that, but what we weren't aware (nor was our GP and the shrink he saw to get diagnosed) was that it would cause ADD symptoms. Sure enough, as soon as the folks started giving him a protein shake every day his symptoms went away.
The point of this is that I think ADD is probably the most over-diagnosed disease in the country right now. I'm sure plenty of kids have it, but I'm equally sure that plenty of misdiagnosises (or quick-fixes at the behest of helicopter parents) are putting kids on meds they don't need to treat a problem that either could be treated and/or cured otherwise, or that they don't actually have.
And finally, as a last parting shot at people who still think ADD isn't real, let me sum up my situation as thus: normally I am an unlikable jackass who interrupts people and can't focus for more than a second. When I take Ritalin, I'm fairly pleasant, complete my work on time and am generally normal(ish). Whatever the cause of my problems, the Ritalin makes it go away. This cannot be disputed. I'd say that pretty much indicates, no, defines my problems as symptoms of a medically treatable condition.