I always get very brief beachballs on every mac and app I use. Sometimes things need to load and a beachball comes for a second or two. I don't see that as a big deal. What I noticed with netflix however is that it pushes the memory pressure up if I let it run for a long time. I suspect silverlight as the culprit.I am also using youtube on html5 and beachball mostly occurs when i have opened lots of tabs with videos. But if i wont make the tab active the video doesnt starts to load.