You cannot use an underscore in the domain name - it's not a permitted character. And in the rest of the file path, the dash is still a stronger separator for keywords than the underscore.
Use hyphens in domain names and periods in host names.
Use hyphens, periods or commas in paths.
Never use underscores or spaces. They always lead to trouble.
In domain names, I'd recommend that you avoid using hyphens ('dashes') wherever possible. I just think that domains are better without hyphens. And as tedster says, you can't use underscores in domains.
In the rest of the URL, I think that using hyphens is fine - I think it helps separate out the URL for the user, and also for the search engines.
Thanks for all the replies.
So, just so I am clear, I should name my new website pages as follows:
bluewidgets.com/free-widgets "not" bluewidgets.com/freewidgets
Thanks in advance for all the help,
Hyphens (not, ahem, the same thing as dashes) are annoying to type. They're off in the corner of your keyboard where you have to hunt and/or reach for them. You don't want to exasperate the users who are so devoted to your site that they can type in the url from memory, do you ;)
As a user, I tend not to like the "look" of hyphens. It's but a short step from "blue-widgets" to "everything-under-the-sun-was-taken-so-I-had-to-go-with-blue-widgets-with-a-hyphen-dot-com" or "I-am-too-lazy-to-work-up-a-rational-directory-naming-system-so-I-will-just-use-the-whole-article-title-no-matter-how-long-it-is".
Back to OP's original re: hyphens v underscores... avoid underscores... period. In Link display they appear to be THIS LINK (a space) instead of THIS_LINK, and when one seeks typed in traffic that's a problem.
but if you want somethingtomakesense in a url you-might-find-a-hyphen useful.
Pick and choose your battles and, and in most cases, less is more.
I think I may have asked my question incorrectly. I apologize for any confusion.
My "home" page will be named:
bluewidgets.com NOT blue-widgets.com
The page where I give away free widgets will be named:
bluewidgets.com/free-widgets NOT bluewidgets.com/freewidgets
Will this be the best way to name the pages of my new site?
First, whenever Cutts recommends anything, he recommends you use it implement it from a user satisfaction standpoint, not SEO.
And typing a hyphen in a domain name is not anything a use likes to do (and most think spam the minute they see such a domain).
What Cutts was referring to in his WebMaster Tools video (which you are referring too) was using hyphens versus underscores in file names. With the latter (an underscore), Google treated it as a unique phrase, whereas the former was treated as a series of keywords.
Cutts recommended hyphens because it is more likely to return a result even if a specific phrase was searched for.