This is a piece from Google's Search Engine Optimization Starter Guide
Good practices for URL structure
• Use words in URLs - URLs with words that are relevant to your site's content and structure
are friendlier for visitors navigating your site. Visitors remember them better and might be
more willing to link to them.
Avoid:
• using lengthy URLs with unnecessary parameters and session IDs
• choosing generic page names like "page1.html"
• using excessive keywords like "baseball-cards-baseball-cards-baseballcards.
htm"
Notice the last line.
It's an example of an excessively long line, but more importantly they do use dashes.
Also I can't find it now, but I'm pretty sure that I did see somewhere on their site that they actually recommend using them.
I use dashes in the urls of my articles all the time and I still get number 1 rankings so I think that they don't hurt, and they may actually help.