Youtube runs fine in Firefox and Internet Explorer, but I mainly use Google Chrome (I’m currently using Version 28.0.1500.72 m) and Youtube is running really slow for me. If I pause the video, buffering seemed to pause too. The solution I found was to go into my Youtube account and disable or opt-out of the “HTML5 Trial” by going here http://www.youtube.com/html5. I have posted a screenshot below to help you know what to look for.
You can also find more discussion on the Google support forum from other users.