Matt Cutt's addressed hyphens and underscores in URLs. If you've already started with underscores (as Wikipedia uses them), don't rush out and change them. Google will understand the difference and still rank you accordingly. You should begin a new site with hyphens, but don't go out and 301 all your old permalinks.
A hyphen is meant to be a separator and an underscore a connector in searches. Google was developed by programmers and it is a lot easier searching programming terms.
This shouldn't be a problem today as many start with WordPress and permalinks are automatically made with hyphens.
If using WordPress, a keyword should be in your title already with researching your main word and creating an enticing title around it. Your title will be converted into a permalink if you have them setup correctly.
A good tip is to include your main keyword, which turns into a long-tail phrase once the permalink is automatically generated upon input. You can see this by looking at the URL of this thread including the title as "url-optimization-tips". Having your own blog or website, you can customize this and should follow this format.
Include the keyword in a H1 tag as well
Good tip, just expanding on it with WordPress as the CMS!
Edit: I must have read your post wrong, I thought it was speaking about permalinks.
This video is very old and urls no longer play such an important part in seo. I know a few years ago it was huge to do "seo friendly" urls. I do not think they matter much any more.
Yes of course URL doesn't play a greater role in SEO. But SEO friendly URL will clearly notifies that what kind of page it is and also it reduces the bounce rate.
look at the serps.
Long urls and short urls rank about the same.
And I doubt that google gives much credence to keyword domains over non-keyword domains.