Yes, I've had so much trouble with this. It's widely contentious especially in children as the symptoms of childhood bipolar can mimic that of ADHD/ADD. I've been strongly suspected of being ADHD as a kid and my old T suspected I was ADD, but I have never been checked for it due to extenuating circumstances.

When I got diagnosed with OCD, the pdoc was leaning towards a BPII DX as well. I have frequently thought about this and my guess is that I might possibly have both. It is hard to point out concrete differences between what I feel to be ADD and what I feel to be BP, but there are some subtle ones known only to me. The main distinguishing factor may be that BP makes me hypersexual as well, though I am not 100% sure that it's not an ADHD symptom as well.