My biggest problem with YT recommendations is that they dramatically overweight recent videos when generating the recommendations. I mean, I can spend a week doing nothing but watching (well, listening) to videos of classical music performances, and my recommendations will be full of classical music, exactly as you'd expect. Then I watch one random one-off thing, like "15 funny pitbull fails" and suddenly ALL of my recommendations are animal videos. Then I have to go manually edit my feed history and remove "15 funny pitbull fails" to get my recommendations back to normal.