Is YouTube a good marketing tool?

I have been wondering for months if YouTube is a good marketing tool. I know if people came across your video it would be a good marketing tool, but most of the time you tube videos are on the second page of google for my desired search terms.

My three questions are:
1) Can you link from YouTube to your site and does it help for SEO?
2) Is there a way to optimize your YouTube page to come up higher on Google?
3) I have a vacation rental web site and would it be beneficial to implement videos into the site somehow?

Just adding a new one, would it be better to take my videos and attempt to implement them into my site or would it be better to have them on youtube?