Something that's been bugging me over the past year or so is a shift in how youtube handles it's compression options with videos that were uploaded at 60fps.
60fps videos no longer have a 1080p30 option at all (format 137), and while there is a 720p30 option (format 136), that format is now being heavily compressed so it's quality is noticeably inferior to the 60fps versions.
When I download videos I like to be sensible with the format options because I might keep the file, or I just don't want the download to take forever. As such I often prefer 30fps but in good quality.
It now seems that the best way to get a good 30fps file from youtube is to download one of the hugely bloated hi-res 60fps files and then recompress it in handbrake. Hardly worth the bother with most things.
More recently, I'm discovering that if I decide to suffer through their web site experience, I can't even watch 1080p videos on my main PC anymore without stuttering and total freezing. Maybe it's because of the VP9/whatever vs h.264 issue mentioned earlier. This computer has never had h.264 acceleration (GTX285 video card) but it was always able to handle it in software until now.