Are you sure it's not a problem with your network?
Try playing youtube videos on a pc.
Yes, I'm sure. I have wired 100Mb internet connection, and I use several VOD online services, samba-shared folders, and local media without any problems. Spicifically, this video tested and plays without stuttering locally, from samba share, from remote http-server folder. Problem appers only with Youtube addon (with any video).