I have been diagnosed with ADHD since age 6, and I can tell you a few things:
1) It is a REAL disorder that DOES affect your daily life
2) It is frequently misdiagnosed by stupid doctors
3) It is about much more than just hyperactivity.
When I was younger, I had much more of the "H" in ADHD (Attention Deficit Hyperactive Disorder for the uninitated), and the medicine did help relax me a little bit. Now in my high school years it's much less the hyperactivity and more forgetfulness. However, the medicine no longer helps me, and I've been on just about all the major pills for it in my life: Ritalin, Adderall, and Concerta. Instead, it just zombifies me and renders me socially inept.
ADHD affects my concentration skills on certain things in that I can only pay real attention to what I'm interested in. Also, I often forget details in conversations and even daily things, like remembering to do chores and such, until I'm reminded. It's pretty annoying.