Youtube is not really optimized for low bandwidth Internet connections nor for slow computer systems like netbooks. Most computer users who access Youtube with that hardware notice that the experience is not as pleasant as it could be. Youtube Feather is a new Youtube Labs project “to serve YouTube video watch pages with the lowest latency possible” by “severely limiting the features [..] and making use of advanced web techniques for reducing the total amount of bytes downloaded by the browser”.
The differences between Youtube feather optimized pages and the standard Youtube pages is quite noticeable. The video playback page of Youtube Feather for instance is fully transferred after downloading 52 Kilobytes of data compared to 391 Kilobytes that the standard pages require.

Youtube Feather achieves this partially by removing standard Youtube features such as posting comments, rating videos, viewing all comments or customizing the embedded player and most problematic of all that not all videos are supported by Youtube Feather.

Some users with the right hardware might on the other hand join the Youtube Feather beta if they are not using those additional features and like a faster Youtube experience. Youtube guests and users can join (and unjoin) the Youtube Feather beta at this Youtube page. (via Google Operating System)
Update: Feather Beta is still available, and YouTube users can join the beta version of the program at the official site. The description does not seem to have changed since it was first announced in 2009, which may indicate that the project has been put on ice by Google.
This is an opt-in beta for “Feather” support on YouTube. The “Feather” project is intended to serve YouTube video watch pages with the lowest latency possible. It achieves this by severely limiting the features available to the viewer and making use of advanced web techniques for reducing the total amount of bytes downloaded by the browser. It is a work in progress and may not work for all videos.
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Hey Martin!
I wanted to share a video about the youtube feather that demonstrates the new feature, that you could post on this article page! it would be perfect showing the new feature. It would help demonstrate it to people.
http://www.youtube.com/watch?v=xLGAm021z1c
thanks so much!
deos not make any changes,, and every time i have to go to the same ;pain to search for it and open it ,,, it is just waste of time