Yep there is a SEO (Search Engine Optimization) for Youtube. Besides the keywords and tags and title, many will want to take it a step further to have the most ideal thumbnail image for the video. The image that users see and decide whether or not to click on it.
Youtube lets the person that uploads a video onto their account pick from 1 of 3 thumbnails. Many have tried to figure out exact HOW Youtube picks those thumbnails from your video clip. Some have said Youtube picks the exact middle frame. Others say it picks from the 1/4th of the way through the video, then 1/2 and then 3/4th.
Well to find out exactly, I did a ton of test videos and uploaded them to Youtube (make sure you keep them as Private, or you will junk up your channel).
I recorded a clock on my desktop for 60 seconds and looked at the seconds hand to see which image Youtube grabbed. (if you do this test take 2 videos, but of TWO different types of clocks, it did get confusing when I had 2 one minute videos of the same clock)
I confirmed that IT IS FAIRLY RANDOM in how it picks the thumbnails!
Why do they do this? Too many peope try to manipulate the system. They edit their videos so a great image flashes during the 1/2 way mark, or 1/4 mark.

So the solution? First of all be generally aware that Youtube is going to pick something near the middle (not exactly in the middle though) and toward the front and toward then end.
1) Upload your video in PRIVATE mode.
2) If you don't like the thumbnail options
3) Delete the video
4) Reupload it.
5) Rinse and Repeat
Other Tips:
- Youtube will not let you upload the same file again, even if it has another filename. You have to either compress it to another format or delete it from youtube and reupload it.
Good luck
Written by Frank
p.s. For those of you in Virginia, check out my agent Ray's www.VideosByAdress.com which is the first MRIS approved Video vender. Soon to be reviewed here. And for now, it is FREE to upload real live Video (vs an animated slideshow of photos) with your MLS listings.
Here is the video demo:
Thanks Frank! The interesting thing about this is that youtube stores all their thumbnails under the web address:
http://img.youtube.com/vi/YOUR VIDEO ID/1.jpg
http://img.youtube.com/vi/YOUR VIDEO ID/2.jpg
http://img.youtube.com/vi/YOUR VIDEO ID/3.jpg
The only thing that changes is the "YOUR VIDEO ID" and everything else stays the same. Ideally, you want to always select the 1st picture because it will show the front of the house (assuming that you start your videos from the front).
Now, the question is, how do you make sure that the thumbnail selected is always 1.jpg? Good question. Apparently this is possible but I have to do some research and get back to you Frank.