Youtube launched a trimmed down version of their site a few days ago called Feather (currently in Beta).

It works for me because I'm by no means any sort of power Youtube user, so I don't mind tossing out any bells and whistles that JavaScript and CSS can provide.

I could tell from the layout that there was fat trimmed, but I wanted to see how much actual code was cut so I cracked open Safari's developer panel (*note that the majority of the grey 'Other' category is the actual video being loaded, so that's going to be the same size in both modes).

normal page size:

Feather page size:

And here are the layout comparisons.

normal page layout:

Feather page layout: