I don't mean to make light of people who do have ADD or ADHD, but I have to say, recently I've been all over with the concentration.
Between continued research for Austria during Napoleon and finishing that story, I've plotted out 2 more. I'm really into this newest one, set to take place during the early stages of Hitler's rise to power. (Research on that is easier than anything Austria related!) But it's just amazing what the average person did, felt, and experienced during that time. It was mass chaos. Wonderful to write about, terrible to experience.
So I flip between the two - Austria 1814 and Germany 1934 - and hope that some weekend I can sit and finish one.