YouTube Feather Beta
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 page 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 page requires.
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 un-join) the YouTube Feather beta at this YouTube page. (via Google Operating System)
Update 2: YouTube Feather is no longer available, and there is no comparable option available at this point in time. The best option that you have is to set the quality of the video stream to low on YouTube.
You do this with a click on the settings icon that is displayed when you hover over the video area on the YouTube website. Select quality, and pick one of the lower quality options displayed there. The lower the quality (read number) the less data needs to be transferred to stream the video. End
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.