I have never been able to tell if a light is on or off on any of my dynohubs. I know there is extra drag, but I don't feel it. I use a sanyo, a really cheap Shimano, and 2 of the top of the line Shimano dynohubs. I can't really tell the difference at all.

I have had the PD8 for over a year now, but I wasn't' riding it until this year. Probably 1000 miles on it by now. I would say our gravel is pretty extreme conditions. I never had trouble with a shimano under those conditions either though.