The symptoms of this are a bit too "catch-all" and difficult to accurately "diagnose" (since it is a syndrome and not a disease with an organic cause) which results, unfortunately, in the inapppropriate and overly-zealous medication of kids; in some day care centers kids arte not allowed to be there unless their parents medicate them...
People past the teenage years should not use Ritalin. Adults with ADD should look into behavior modification and therapy for this. Often the very basic problems one experiences can be addressed quite directly.
I have it, too, and have had it since I was a kid, though no one understood it, then. I was the "dreamy kid looking out the window bored in class and not paying attention to the rules of how to play softball" rather than the "hyper troublesome kid who does poorly in school" type...I did have emotional and temper problems, too, but this may have been a function of the environment I grew up in (though I was more troubled than my siblings when very young). I was very successful in academics and school activities, though a bit of a loner for years...
The "dreamy" ADD kids kids often turn into highly creative intelligent adults who have trouble functioning in "normal" social situations (they misread cues because of focus problems, NOT in the same way of Asperger's Syndrome, for whom social cues are often unreadable), and who have problems with organization, motivation, procrastination, focus and follow-through. This can create problems with professional advancement, money, and relationships, just for starters. They may have what appear to be highly-disordered surroundings, but certain aspects of their lives are highly-controlled.
A great book on it is Driven to Distraction, by a doctor who specializes in diagnosis and treatment in kids and adults...