YouTube recently has added a orkut sharing button to the list of sharing thumbnails. Previously, you had to copy & paste the video URL to post the clips to your orkut favorite videos. Now you can simply share your favorite videos using orkut sharing button directly from YouTube.
Previously, YouTube promoted only 2 social networks - Myspace and Facebook - so now with adding the orkut thumbnail.
YouTube now promotes orkut as well as the other ones, even though Google owns orkut.