The race to 1000 subscribers
Audience retention is now king and making sure that your video gets watched and watched all the way through.
Watch Time At this present time it is the number one ranking factor affecting your video and the success of the other videos on your channel.
Session Time affects the rank and surfacing of individual videos as well as on a channel-wide level
Tom Martin has great tips over at http://www.faqtube.tv/youtube-video-optimization/
With more and more search and entertainment being conducted through mobile search and streaming video marketing messages need to have and be video friendly and relevant to consumer demands.