One of the feature requests that we've received most frequently from developers it to have a YouTube API call that enables or disables commenting for videos. It's a logical request — videos can be automatically uploaded via the API, and having to visit youtube.com from a web browser to modify the commenting settings manually doesn't make much sense.
We've taken action on this feature request, and gone one step further: the new <yt:accessControl> element lets video owners enable or disable video rating, comment voting, video responses, and off-web syndication in addition to commenting. We've also taken an existing element for controlling embedding, <yt:noembed>, and migrated its functionality to <yt:accessControl>. Existing code that uses the <yt:noembed> element will continue to work as per our API deprecation policy, but <yt:accessControl> is preferred for new development.
You can set access controls for a video when uploading or updating a video. See the Setting access controls for a video section of the Developer's Guide for more information.
With the addition of the this feature, the YouTube API now offers parity with all the settings available via the YouTube web interface. We hope that applications that support YouTube uploads take advantage of this new functionality, and we know your users will appreciate it!
-Jeff Posnick, YouTube API Team