I forget sometimes that not everyone has been around the net for ever!
The visitor in question did not realize that you have to click on the COG ICON bottom right of the YouTube video (after you press play) and from the popup menu select 720p or if available 1080p before the clip is actually shown in HD.
Also if you do not want distracting text and links on the screen while you watch your video stream, set Annotations to off after you have set your preferred video quality.
When watching photography tutorials annotations often provide useful links to the photographer’s tutorials, images and video links.
Thanks for the mail – hope this helps 😉
** If you have a slow net connection then 480p might be the best setting for you **