I covered this on Friday at Search Engine Land (so stop reading if you read it there).
YouTube has added a ranking factor to YouTube Search - the new ranking factor is time watched.
Now, depending on how much time your video is watched (I guess based on the video length), the longer the whole video is watched, I guess the more likely your video will rank well in YouTube's search results.
YouTube also added time watched to YouTube Analytics so video producers can see how well their videos are doing in terms of time watched.
Here are some stats from the videos on my YouTube channel:
Friday's Video:



Forum discussion at Google+.

Comments:
patrick sexton
10/15/2012 01:23 pm
of course it can be spammed. it is only a matter of time... here are some ways to spam it... 1. Pay people to watch it 2. Watch it using proxies 3. Use a cliffhanger... "at the end of this video i tell you how to make a million zillion dollars or you could... Wait for it.... Here it comes... Make the thing interesting enough to actually watch
Travis Van Slooten
10/15/2012 03:22 pm
I always suspected that time watched was a ranking factor. It's nice to see it's "official." As Patrick Sexton has noted, now that this is a known factor, it's going to get spammed to death. Looks like I'll have to start a new Fiverr gig (only kidding...lol). Travis Van Slooten
Syed
10/15/2012 03:49 pm
If it wasn't already part of the Youtube algo I would be really, really suprised
vivek
10/16/2012 11:12 am
its part of the Youtube algo....
Murthy Seo
10/16/2012 12:40 pm
It's really interesting updates. The calculation may be video length * visits duration while see the video. The total minutes include having interrupt for something to stop without full length video that means someone close the video or browser without seeing full video.