This is why I don't allow cookies to youtube... or anywhere if I can help it.
It wasn't long ago that I was obsessed with having local copies of videos that I might want to rewatch. This lead to a lot of little scripts that kept increasing in complexity until I was writing my own clients based on reverse engineered specs. But after I lost most of my saved videos in a hard drive crash, I realized that I never watched most of them. And the ones I did were on youtube anyway.