These are interesting discussions of ADHD with links to EP. I'm not so quick to discount the "hyperfocus" aspect with some ADHD patterns. I see this symptom often with some child and adult patients and associates with ADHD. Some of these individuals have little or no evidence of or family history of affective disorder. Essentially, the symptom seems to involve trouble with flexible shifting of focus when the individual is highly stimulated (maybe thru an ideational channel such as an investigator* loosing track of hours while on a project, or a computerphile doing the same). I think this is not the same thing as a similar but independent trait of psychological "absorption."
Another concept I find critical in understanding ADHD is that there undoubtedly are varieties of ADHD, forms, or types. Denckla, for example, suggests that one day we may understand ADHD as a family of disorders as is known for epilespy now. One may take a list of executive functions and trace their expression, if extreme or disordered, in terms of cognitive, affective, and behavioral spheres. This will generate varying patterns of ADHD behavior that can meet the criteria but range quite a bit in phenotype.
Many yougsters brought to the clinic or the office for ADHD concerns will have more behavior disruptive/ externalizing problems. However, ADHD Inattentive Type is more "quiet" and often missed--at times even by experts. The associations with ODD, CD, and Mania would not seem nearly so relavent or common. Another critical variable is to parse out conceptually the role of temperament from ADHD. For example, an introverted and temperamentally anxious individual with ADHD will look much different from the stereotypcial "hyperactive kid." Finally, I find and continue to find in my psychotherapy caseload many adults with ADHD although the more conspicuous symptoms may be muted, and affective problems, other traits, and other life problems have overshadowed discernment of the ADHD syndrome by themselves, others, and myself at times.
Finally, as you are probably aware, Tom Brown, an active champion of the ADHD self-help movement, has written of "hunters and farmers": people with ADHD and those without it. He uses popular notions of evolutionary thinking to place an evolutionary psychology context onto ADHD.
Mark Waugh, PhD
*I have known clinically and personally accomplished scientists (physicists, biologists, etc) with ADHD- Inattentive type who are known for their hyper-focus in their ideational work; although they get alot done at times, not surprisingly, it comes at a cost at other times (e.g., interpersonally).