Had a issue over the last few days with Safari and Youtube. I would be able to play flash video on other sites but on Youtube nothing. Not even the hint of a player loading. Except when I went to a Channel page!
It turns out the problem is when the browser gets to the Youtube page there is some communication so youtube knows the type of browser and sends the video. Well for some reason it stopped on my macbook, they decided to have a time out and not talk. On my other computers it worked ok. But in looking up the problem in the forums it wasn’t just me. The fix is simple and on my mac I went the the info tab for Safari from the applications folder. Then just clicked the 32bit check mark, youtube works again; I presume it will be fixed on next update!!