The first channel that is offering this service is President-elect Barack Obama's YouTube channel, ChangeDotGov. Visitors to the channel can simply use the 'click to download' link above the any video on the channel, to download the clip in high-quality MPEG4 format.
Previously, YouTube users could download clips from the site only by using a separate program, but this required users to also invest in a further application that could play .flv files - not a very common multimedia format. However, Google, which owns the video-sharing site, is considering extending the download function to other channels on YouTube.
"YouTube is rolling this out slowly, initially with content that aspires to be consistent with principles of open government." Lessig also added that YouTube video download will "be offered more generally". How 'generally' though, is not yet known.
But this leaves enough space for speculation. Some say YouTube's video download capability will be limited to user-generated videos only.
On the other hand, it's likely this new feature will expand across YouTube, though disabled by default - in order to prevent copyrighted content from being downloaded. But most probably, it will be the users who will decide in the end whether they want to allow viewers to download their content.
See also: Watch YouTube on your PS3 or Wii