SEO rules are always changing. Google is constantly improving their software to 'root out/remove' websites that 'cheat' by adding non-relevent content to get better seo. Long term, the best advice is to structure your site well and have lots of original content thats relevant to your websites subject. google will recognize and reward good websites, and penalize poor ones. Short term gain may lead to long term pain.
Video posting is an excellent method of promotion. Video posting on You tube may not improve your SEO as I am not sure google currently 'count' the links from youtube.com as 'backlinks'. But, by using it and the other sites like vmeo, daily motion and these others(whos links DO count i believe) you can attract many new people to your site. Use the video descriptions, use good keywords.
You may not get the magic top link on google from them but they will definitely be worth your effort. Good old fashioned hitting the pavement and doing leg work to get people to your site.
Here's some Youtube alternatives
nichestealth.com/social-media/top-8-youtube-alternatives
If you're making a presentation slideshow video, check out
animoto.com
You can be up an running in a few minutes if you have some images handy and some slogans to use.