In the Google hangout from last week on Google+ at the 17:50 minute mark John Mueller of Google said that keywords in the URL is a "very small ranking factor."
The question: "Keyword in the URL, is that a ranking factor?"
The answer:
I believe that is a very small ranking factor. So it is not something I'd really try to force. And it is not something I’d say it is even worth your effort to restructure your site just so you can get keywords in your URL.
Here is the video embed:
Note, this is nothing new, we covered it back in 2006, and we ran a poll in 2009. Google has said it is not worth changing your URLs to get keywords in them.
So if you build a new page or site, then go with keywords but don't spam it out.
Forum discussion at Google+.