Ok, here's my honest and informed opinion, so please don't flame me...
I have noticed with several of my friends, the occurrence of what I call ADHD discrimination. What usually happens is that someone gets "clinically diagnosed" (as in a "doctor" signs a sheet of paper that goes in your medical record), and suddenly doors are slamming in their faces.
One friend of mine was on the fast track for the Navy's nuclear program with great test scores and everything. He started having headaches and trouble concentrating, got sent to the local psych and was promptly labelled ADHD. Shortly thereafter he was dropped from the nuclear program and spent the last 5 years of his contract restocking vending machines and doing laundry on aircraft carriers (no joke).
Acquaintance #2: Commercial transport airline pilot flying for a small shipping company. Fresh out of flight school (well a few years, but still under 30). Found himself falling asleep and having trouble concentrating on long flights. Surprisingly, not a critical problem, but still a concern. Got "diagnosed" with ADHD and lost his job immediately thereafter... Later found out that it was from a lack of oxygen in the cockpit (a design flaw in the plane that affected other pilots as well). He still hasn't outlived an incorrect diagnosis and now works for the Air National Guard training others for comparative pennies...
Girl, #3: Accounting graduate. Lost 3 jobs during orientation after hiring company found out she had been diagnosed with ADHD as a child and was on prescription medication for said condition. Kept her mouth shut on interview for job #4 and is still employed, however, she is in constant fear of losing her job in IT corporate finance if someone discovers her "secret".
I would highly recommend against getting "diagnosed" with anything that could negatively affect you in the long run.
The sad fact is that when people hear ADD or ADHD, they think, slackers, hyper, unattentive to detail, uncontrollable, poor workers, poor students, handicapped, etc...
I myself was misdiagnosed with a heart defect 5 years ago. Come to find out that I developed an allergy to pseudophed (an allergy medicine ironically) and it was causing heart palpitations. Consequently, I also became allergic to caffeine, a similar type of stimulant. I lost my pilot's license as a result and only after extensive testing and the threat of a lawsuit did the FAA give it back...
The moral of the story is this: If you have a serious problem, by all means seek help. But be wary of anyone trying to slap a label on you that could alter your life so radically. Things like ADD/ADHD, depression, mood disorders, etc. are often labels used when doctors really don't know what the hell is going on. Sadly they can ruin your life when misused...
I personally believe that they are merely "conditions" invented by drugs companies to addict people to their drugs. They create a problem and then provide a "solution" (often an expensive and recurring one at that)...
Yikes!