@YouTube really bugs me at times. It used to be that when you had watched a video the thumbnail for it would be grayed out with watched across it. Then they changed it to this daft red bar along the bottom of the video that showed how much of the video you had watched.
I did voice my concern about the change when it first changed, as I have some problems with my sight I find it hard to see these red bars. The watermark style with watched across the thumbnail was far better, but that's just me.