Recently, Youtube had a feature showing a playlist of songs that you could go through. The first time I checked this out I was thinking, "Man, whoever compiled this playlist is a genius. They have all the great songs here." Then I realised that the playlist is generated based on your viewing history.

I used it a few times thereafter but now I can't find it. Maybe they got rid of it. I was surprised that they had this feature to begin with. Although, I guess copyright isn't really a problem nowadays because Youtube let's copyright holders claim videos and get the ad revenue.