From reading the blog it appears that producers can now use the system to add captions to their videos, and users can use it on non-captioned video too.
You can read a blog of the press conference at CNET.
UPDATE: I just went to look at my videos on YouTube, and there's a Machine Translation button (which is labelled "Request Processing (English only)" )and has the following disclaimer:
Machine Transcription is available for the videos in this Channel. To enable Machine Transcription for this video, please 'Request Processing'. We will try our best to get some results in a few days.