To recap, video thumbnails are appearing more and more in Google's "Universal" or blended search results. Not only that, people search specifically for video in Google Video vertical search - even about commercial products. So it's important to optimize the video you worked hard to create.
Once you've turned from your video SEO sins (the common mistakes webmasters make), it's time to go above and beyond to improve the chances of video from your domain appearing in Universal Search and video search.
1. Build links to your video landing pages
Just like traditional SEO, links to landing pages with video content can help your videos rank higher in Universal Search. Links help boost your PageRank, which Google uses as a measure of "authority" or popularity of your page. Because Universal Search displays only 2 video search results, this is very important.
Internal links (which exist on your site in menus, product listings and contextual links) count, but in a different way than inbound links from other sites - inbound links are more valuable. If you have an affiliate program, use SEO-friendly affiliate links (if possible). Or, include links back to your landing page in the embed code you provide for those who want to re-post your videos. Example:
You can add links to Youtube video descriptions linking back to your site, but it won't help you with SEO. Such links have a rel="nofollow" attribute attached to them, which prevents the search engine from following them.
While it's best to have links pointing at the video landing page, any links pointing to your domain can help raise your site's "authority," which will benefit all your site pages - provided they're followed links from sites that Google deems good quality and topically relevant.
2. Use a transcript
The text surrounding your video helps search engines understand what your video is about, since search engines can't "hear" the audio. A transcript contains all the narrative - which adds valuable keywords to the page. However, a transcript might clutter up a product page that already has a description. To help with SEO, the text must appear on-page, not in a separate link or pop-up. (You might hide it behind a tabbed box). A transcript is not the best choice for every video - your discretion is advised.
3. Allow comments on your video / reviews section
People who comment on video sites like Youtube enrich the page with keywords, including variant ways of describing products, usage scenarios and even typos (yes, typos can help you rank for the typos searchers use, like "Odacity of Hope"). Product videos are not necessarily the type of media people like to comment on (unlike an entertaining or educational clip). But that's fine, the existence of customer reviews can have the same SEO-boosting effect.
4. Provide closed captioning
Not only will you attain sainthood by improving accessibility for hearing impaired and volume impaired (*cough* employees surfing the web on company time), Googlebot can also read closed captioning on your video. (This does not mean that Yahoo or Bing can).
Another reason to CC, President Obama just signed a bill into law that will require producers of online video to provide closed captioning.
Indirectly, CC can help SEO when your content is linked to by the hearing impaired community as an accessible site.
5. Syndicate wisely
It's easy for Youtube and Vimeo and the rest to outrank videos that live on your domain if you've syndicated them widely. My recommendation is to submit to a maximum of 3 sites, and to provide custom title tags descriptions for each to prevent duplicate content in search engines. You will still be competing against them for ranking, but you are less likely to be caught by a duplicate content filter if it appears the content is unique across sites (remember, Google can't see the video itself is the same). Make sure you link back to your site in the syndicated descriptions. Though most video sites will nofollow your links, you still can direct customers to your site.